1941 Onderstepoort Journal of Veterinary Science and Animal Industry, Volume 17, 1941

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Contentes Pages: Onderstepoort Journal of Veterinary Research, Vol ??, 19??

CONTENTS

Volume 17: Numbers 1 & 2

Section I: Bacteriology

Treatment and control of chronic streptococcus mastitis in bovines: results obtained in two herds	Van Rensburg, SWJ & Thorburn, JA	7

Section II: Parasitology

Ticks in the South African zoological survey collection - Part I - Ixodes alluaudi Neumann 1913, a primitive tick parasitic on shrews	Theiler, G	51

Section III: Physiology

Studies on the alimentary tract of merino sheep in South Africa. VI. The role of infusoria in ruminal digestion with some remarks on ruminal bacteria	Van der Wath, JG & Myburgh, SJ	61

Studies on the photosensitisation of animals in South Africa. XI. The reaction of the sensitised Merino skin to radiation in different regions of the spectrum	Riemerschmid, G & Quin, JI	89

Section IV: Sex Physiology

The hydrogen-ion concentration of the vaginal secretion of merino sheep during oestrus, dioestrus, and pregnancy, with some remarks on its influence on sex-determination, and the influence of the vaginal temperature at the time of mating on conception	Quinlan, J, Myburgh, SJ & De Vos, D	105

A note on the results of an attempt to fertilise native goat-ewes with sheep-rams	Quinlan, J, Roux, LL, Van Aswegen, WG & De Lange, N	115

Further observations on the scrotal skin temperature of the bull, with some remarks on the intra-testicular temperature	Riemerschmid, G & Quinlan, J	123

Thermocouples for temperature measurements on skin surfaces and in living tissue	Elder, JS	141

Section V: Nutrition

The relative digestibility of the constituents of the carbohydrate complex of grasses at successive stages of growth with reference to their partition into crude fiber and nitrogen-free extract according to the standard method for feeding stuff analysis	Louw, JG	165

Section VI: Pharmacology and Toxicology

South African Senecio alkaloids. Part 6. The toxic alkaloids of Senecio sceleratus sp. nov. Schweikerdt	De Waal, HL & Pretorius, TP	181

The hydrocyanic acid content of Cynodon plectostachyum Pilger (Giant Star grass) and its suitability as a pasture grass	Van der Walt, SJ & Steyn, DG	191

Poisoning by voided urine	Van der Walt, SJ & Steyn, DG	201

Poisoning by spent calcium carbide	Van der Walt, SJ & Steyn, DG	207

Recent investigations into the toxicity of known and unknown poisonous plants in the Union of South Africa. XII	Van der Walt, SJ & Steyn, DG	211

Section VII: Pathology

Domsiekte or pregnancy disease in sheep. I. A review of the literature	Groenewald, JW, Graf, H & Clark, R	225

Domsiekte or pregnancy disease in sheep. II	Groenewald, JW, Graf, H, Bekker, PM, Malan, JR & Clark R	245

Section VIII: Zootechny

Preliminary observations on the breeding of ferrets in South Africa	Murray, GN	297

Section IX: Wool Research

Studies on the variation within the fleece of the characteristics of South African Merino wool. I. Tensile strength	Van Wyk, CM	311

Studies on Merino wool production. Plainbodied and developed Merino sheep. I. The standard of production of a group of plainbodied stud ewes	Bosman, V	319

Studies on Merino wool production. Plainbodied and developed Merino sheep. II. Fleece density tests on a group of extremely plainbodied Merino stud rams	Bosman, V	345

Section X: Anatomy

Anatomical studies no. 65: Two cases of cervical ribs in bovines	Cloete, JHL	351

Author index		365

Subject index		367

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Subject index
(Published by The Government Printer, Pretoria, 1941) Anonymous; Du Toit, P.J.
Author index
(Published by The Government Printer, Pretoria, 1941) Anonymous; Du Toit, P.J.
Anatomical studies no. 65 : Two cases of cervical ribs in bovines
(Published by The Government Printer, Pretoria, 1941) Cloete, J.H.L.; Du Toit, P.J.
After giving a description of two instances of cervical ribs in bovines, these cases are considered in the light of various theories that have been advanced in explanation of such anomalies. It is concluded that both of them are covered by the atavistic or reversionary theory, which is here specifically defined as indicating that heredity has supplied the material from which, through stimulation probably emanating from the organism’s environment, there develops a structure resembling that which was normally present in an evolutionary ancestor.
Studies on Merino wool production. Plainbodied and developed Merino sheep. II. Fleece density tests on a group of extremely plainbodied Merino stud rams
(Published by The Government Printer, Pretoria, 1941) Bosman, V.; Du Toit, P.J.
The analysis of the fleece densities of a group of extremely plainbodied stud rams is given. The number of fibres growing per square inch of skin (shoulder) varies from 29,100 to 53,200 with a mean of 40,900. The fleece densities expressed as the per cent. skin area occupied by wool fibre varies from 1.58 per cent. to 3.06 per cent. with a mean of 2.38 per cent. It is concluded that extremely plainbodied stud rams can produce a good stud standard of fleece density.
Studies on Merino wool production. Plainbodied and developed Merino sheep. I. The standard of production of a group of plainbodied stud ewes
(Published by The Government Printer, Pretoria, 1941) Bosman, V.; Du Toit, P.J.
The wool production and fleece analysis of 50 extremely plainbodied stud ewes are given. The ewes were typical of the sheep of the stud (including the stud rams) and were obtained from a breeder who had consistently bred for extreme plainness, so that this characteristic is successfully being transmitted to the progeny. Thirty-five four-toothed stud ewes, recorded in 1940, gave an average greasy fleece of 13•28 lb.; a clean scoured fleece of 7•47 lb. as bone dry, or 8•7 lb. at 16 per cent. Regain; a yield of 58•4 per cent as dry or 67•7 per cent. on the the Bradford system; an average staple length of 4•0 inches and a 60's quality number with a coefficient of variability of 4•5 per cent., indicating a uniform group. The number of fibres per square inch of skin ranged from 31,700 to 45,000, with an average of 41,600. The average fleece density was 2•51 per cent. Fifteen four-toothed stud ewes, recorded in 1941, gave an average greasy fleece weight of 12•17 lb. with 6•99 lb. of clean scoured wool as bone dry, or 8•1 lb. of clean wool at 16 per cent. Regain. The yield was 58•1 per cent. as dry or 67•3 per cent. on the Bradford system. The average staple length was 3•8 inches and the quality number a 60's with a coefficient of variability of 4•3 per cent. showing a uniform group. The number of fibres growing per square inch of skin ranged from 30,200 to 71,600 with an average of 46,700. The average fleece density was 2•54 per cent. It is concluded that the extremely plainbodied stud here described possesses a good stud standard of production in regard to the total wool, the length, and the fleece density. The view held by many sheepmen that extremely plainbodied sheep must necessarily have inferior fleeces, cannot be substantiated. Not only do these sheep produce profitable fleeces, but by virtue of their smooth skins and strong constitutions, they possess the practical advantages of the plain bodied type. The reliability of judging merino wool production in practice is discussed. It is contended that the judgment of fleece density and quantity of wool is difficult because of the grease factor and an increased need for fleece testing has been experienced. In the stud analysed there is a highly significant correlation between greasy fleece weights and scoured fleece weights and an insignificant correlation between greasy fleece weights and yield. In consequence, the breeder can, by selecting the highest greasy fleece weights, automatically improve upon the clean wool production. This recommendation does not hold where there is a definite relationship between greasy fleece weights and yields.
Studies on the variation within the fleece of the characteristics of South African Merino wool. I. Tensile strength
(Published by The Government Printer, Pretoria, 1941) Van Wyk, C.M.; Du Toit, P.J.
The tensile strength of the wool grown on six regions on each of eight sheep was determined. Significant differences between the regions were obtained. In all eases the tensile strength of the belly wool was considerably lower than that of the rest of the fleece. This point was further investigated with six groups of ten sheep each, and it was found that in the case of every group the shoulder sample had a higher tensile strength than the belly sample, the mean difference being highly significant. This finding strengthens the National Wool Growers' Association's recommendation that belly wool should be baled and sold separately from the rest of the fleece. It was further suggested that the belly wool should be excluded in assessing the average tensile strength of the wool of a sheep. Differences in tensile strength between the wool from other regions of the sheep were found to be insignificant, but the highest values were obtained on the shoulder and back and the lowest on the thigh. It was concluded that the shoulder sample should be used for assessing the tensile strength of the wool grown by a sheep, especially in comparisons between different sheep, since differences between the value for the shoulder sample and that of the whole fleece showed the smallest variability. The total correlation coefficient between tensile strength and fibre fineness was -0•4168, a highly significant value.
Preliminary observations on the breeding of ferrets in South Africa
(Published by The Government Printer, Pretoria, 1941) Murray, G.N.; Du Toit, P.J.
The ferret fits in immediately with its new environment as regards its sexual cycle, when taken from the northern to the southern hemisphere. The animals that were in anoestrum in England started breeding shortly after they arrived in South Africa - the last litters being born the 22nd March, 1938. Females may be stimulated to show oestrus, even where the light is decreasing, after the birth of a litter or after they have suckled their young for some time. A female may even remain in oestrum throughout the winter. There is, however, a big variation in the reaction of different females. Some females that had litters during December did not show oestrus again during that season while other females still came on heat as late as the end of April after their young had been weaned. Fertile matings appeared to occur only until the end of January or the first week in February. A few matings occurred after this date, but no young were produced. The earliest that a litter has been produced is the 6th September. This female was served on the 27th July, 1940, so that litters have been obtained from September to March inclusive. The breeding season at Onderstepoort, therefore, appears to be about 1 to 2 months longer than in Europe. Young males, born during the previous season, will copulate and are fertile about a month earlier than older males. When females commence to come on heat toward the middle of July, only young males will sense them. The average litter size of those in which one and more have been reared is 6•0 young per litter and 5•7 in those litters of which all the young were destroyed. If females are served immediately after their vulvas start to swell, then the average litter size is only 3, which is half the normal. The average litter size of the previous litters of these females was 9, so that early service can reduce the litter size to half or a third the normal size. Up to the end of November only 10 young out of 177 were reared. From December there was an improvement. It appears that the months September, October and November have an adverse influence on the mothers and probably on the young as well. This is substantiated by the results obtained with rats over a period of 4 years. During this time of the year the survival rate is the lowest and those that did survive grew at a slower rate and did not reach the same mature weights as those born during the favourable time of the year. Experience during the last two years indicates that there is very little advantage in breeding ferrets before November, although they commence to come on heat 3 months earlier. Rats born during June and July have done very well. Therefore it is intended to try out the practicability of electric lighting for large scale breeding and probably injecting only the males with pregnant mare serum after they had been exposed to the extra light for some time.
Domsiekte or pregnancy disease in sheep. II
(Published by The Government Printer, Pretoria, 1941) Groenewald, J.W.; Graf, H.; Bekker, P.M.; Malan, J.R.; Clark, R.; Du Toit, P.J.
Undoubted cases of Domsiekte have been produced by suddenly cutting the ration of good conditioned heavily pregnant ewes. An identical condition has been set up in non-pregnant ewes but a much longer period on the poor diet was necessary than in the pregnant ewes. Details of the diets, loss of weight of the animal, clinical symptoms, chemical analysis of the blood and urine, pathological changes and blood changes are recorded. There is no doubt that the Domsiekte produced is identical with the "Pregnancy Disease" reported from other countries.
Domsiekte or pregnancy disease in sheep. I. A review of the literature
(Published by The Government Printer, Pretoria, 1941) Groenewald, J.W.; Graf, H.; Clark, R.; Du Toit, P.J.
The available literature is reviewed and where possible conclusions are drawn. References are listed which deal either directly or indirectly with the question of Pregnancy Disease of sheep.
Recent investigations into the toxicity of known and unknown poisonous plants in the Union of South Africa. XII
(Published by The Government Printer, Pretoria, 1941) Van der Walt, S.J.; Steyn, D.G.; Du Toit, P.J.
The toxicity of fourteen plants was investigated. According to the available literature the following plants, viz., Mesembryanthemum angulatum Thunb., Kalanchoe rotundifolia Harv. and Urginea rubella Baker have for the first time been proved to be toxic. The results of the experiments with the fungus-infected mangolds and Scilla oratifolia Baker form. cannot be considered conclusive. Poinciana pulcherrima L. was shown to be a cyanogenetic plant and it was proved that Ornithogalum thyrsoides Jacq. is capable of causing blindness.
Poisoning by spent calcium carbide
(Published by The Government Printer, Pretoria, 1941) Van der Walt, S.J.; Steyn, D.G.; Du Toit, P.J.
(1) Poisoning by completely spent carbide is very similar to poisoning by calcium hydroxide. (2) So-called spent carbide may contain active carbide which, when ingested (moistened), will yield acetylene. Furthermore, other impurities such as ammonia, sulphuretted hydrogen, phosphine and cyanamide may also be present. (3) In our experiments no evidence was obtained that any impurities of any toxicological importance were present in the spent carbide with which the experiments were conducted. (4) Since a relatively large quantity of calcium hydroxide is necessary to poison an animal it is obvious that the calcium content of the stomach contents will be greatly increased in cases of poisoning by this substance. Consequently the determination of the calcium content o£ the stomach contents may be of great assistance in determining whether an animal was poisoned by spent carbide.
Poisoning by voided urine
(Published by The Government Printer, Pretoria, 1941) Van der Walt, S.J.; Steyn, D.G.; Du Toit, P.J.
The hydrocyanic acid content of Cynodon plectostachyum Pilger (Giant Star grass) and its suitability as a pasture grass
(Published by The Government Printer, Pretoria, 1941) Van der Walt, S.J.; Steyn, D.G.; Du Toit, P.J.
South African Senecio alkaloids. Part 6. The toxic alkaloids of Senecio scleratus sp. nov. Schweikerdt
(Pretoria : The Government Printer, 1941) De Waal, H.L.; Pretorius, T.P.; Du Toit, P.J.
(1) Senecio sceleratus sp. nov. 'Schweickerdt is an extremely toxic Senecio species. It contains at least three more or less toxic alkaloids, viz., isatidine, retrorsine and a new alkaloid, sceleratine, (2) Sceleratine, C₁₈H₂₇O₇N, crystallizes with one molecule of water of of crystallization from water and apparently three molecules of ethanol of crystallization from ethyl alcohol. M.P. 178°C, [α]D/21 = +54·0° (ethanol). (3) Upon catalytic hydrogenation sceleratine undergoes hydrogenolysis at the B-hydroxyl and retronecanol and sceleranecic dilactone acid are isolated. (4) Hydrolysis of sceleratine leads to the isolation of the well-known necine base, retronecine and a new dilactone necic acid viz. sceleranecic acid. (5) Sceleranecic acid has the formula C₁₀H₁₄O₅, the m.p. 156°C. (also 213°C.) and [α]24/D = -9.3 (water). (6) Sceleratine is bitter, fairly soluble in water and readily forms addition compounds with hydrochloric acid, nitric acid, picric acid, perchloric acid, methyl-iodide and aurichloride. (7) Experiments to determine the relative toxicity of the alkaloids mentioned are being carried out.
The relative digestibility of the constituents of the carbohydrate complex of grasses at successive stages of growth with reference to their partition into crude fiber and nitrogen-free extract according to the standard method for feeding stuff analysis
(Pretoria : The Government Printer, 1941) Louw, J.G.; Du Toit, P.J.
The structural constituents, natural cellulose, hemicelluloses and lignin, in graminaceous food materials, faeces, and the crude fibre isolated from these have been determined. The results showed that: (1) crude fibre is almost wholly composed of natural cellulose but that the method for its isolation underestimates the natural cellulose content of the feed and of the faeces; (2) natural cellulose is the most digestible portion and lignin the least digestible portion of the cell-wall structure. From this finding it is inferred that a closer association exists between the lignin and the hemicelluloses than between the former and the natural cellulose of the cell-wall complex; (3) with regard to roughages the standard feeding stuffs analysis does not divide the carbohydrate complex into substances of relatively low and substances of relatively high digestibility.
Thermocouples for temperature measurements on skin surfaces and in living tissue
(Pretoria : The Government Printer, 1941) Elder, J.S.; Du Toit, P.J.
Details have been given of the construction of thermocouples suitable for temperature measurements on skin surfaces and in living tissue. The sources of error have been discussed, and tests of the accuracy of the method have been described. It is concluded that, with adequate precautions, the following degree of accuracy was attained : Skin Surface Instrument - Random errors, ±0·14°C.; systematic errors, less than - 0·2°C. per 10°C. temperature difference between skin and surroundings. Hypodermic Instrument - Random errors, ± 0·1°C.; systematic errors, less than 0·1°C. per 10°C. temperature difference between tissue and air.
Further observations on the scrotal skin temperature of the bull, with some remarks on the intra-testicular temperature
(Pretoria : The Government Printer, 1941) Riemerschmid, G.; Quinlan, John; Du Toit, P.J.
1. The temperature of the scrotal surface has been recorded at various air-temperatures within the range 10°C. to 40°C. (50°F. to 104°F.). 2. At low air-temperatures (10°C. to 25°C.) the temperature on areas I, II, and III gave a mean value of 32.0°C., 31.0°C., and 33.0°C.; at high air-temperatures (25°C. to 40°C.) the same areas were 33.9°C., 33.8°C., and 36.7°C. 3. Readings (28) of the skin-temperature underneath the hairy coat, taken simultaneously, gave mean values of 33.6°C. at low air-temperatures and 36.5°C. at high air-temperatures. 4. The mean body-temperature at which the high temperature group readings (15) were taken was 38.6°C. 5. Scrotal temperatures at areas I and II increased almost similarly with increasing air-temperature, i .e. slow increase at low air-temperatures (0.06°C. and 0.09°C. per 1° air-temperature increase) and more rapid increase at high air-temperatures (0.29°C. and 0.26°C. per 1° air-temperature increase). Scrotal temperatures of area III and skin-temperatures increased similarly with increasing air-temperature over the whole range of 10°C. to 40°C. air-temperature. The rate of increase for scrotal area III was 0.43°C. at 10°C. air-temperature, and 0.11°C. at 40°C. air-temperature. The rate of increase in the skin was 0.56°C. at 10°C. air-temperature, and 0.14°C. at 40°C. air-temperature. 6. The degree of contraction and relaxation of the scrotum, as indicated by its length from the dorsal to the ventral extremity, gave a mean value of 24.2 cm. at low air-temperatures and 29.0 cm. at high air-temperatures, a difference of 4.8 cm. 7. From limited observations on the body-temperature, at high air-temperatures only, there appears to be a highly significant relationship between the body-temperature and that o£ the air and scrotal areas I, II, and III. There was no significant relationship between body and skin-temperature. 8. An observation was carried out at artificially created low air-temperatures. The bull was exposed to a temperature of 4°C. to 6°C. for six hours. 9. Under these conditions scrotal area I increased immediately from 30°C. to 33°C. It then decreased and fluctuated between 31°C. and 32°C. During the following 4 hours, scrotal area II always showed lower temperatures than area I (up to 3°C.) . Scrotal area III increased markedly at the beginning and then showed a slight tendency to decrease, but after one-and-a-half hours remained 2°C. to 4°C. lower than skin-temperature. 10. There was marked shivering, which began one-and-a-half hours after exposure, and continued until one-and-a-half hours after the bull was removed from the cooling chamber. 11. The pulse rate per minute varied from 66 to 62 in the cooling chamber and dropped from 64 to 58 within an hour after removal. 12. The respiration count was 16 per minute after six hours exposure and 13 per minute one hour after removal. · 13. The skin-temperature showed steady increase, up to 35°C. (air-temperature 4°C.). It then decreased continually to 32.6°C. at the end of the experiment, but a constant level had apparently not been reached. After removal from the cooling chamber, there was an increase of 3°C. within an hour. 14. The length of the scrotum decreased with a fall of scrotal and skin-temperature during exposure. There was marked relaxation upon removal to higher air-temperature. 15. The body-temperature increased by 1°C. at the commencement of exposure, and remained remarkably constant at about 39°C. throughout the exposure and after removal from the cooling chamber. 16. The intra-testicular temperature, measured with a thermo-needle, at an air temperature range of 15·2° C. to 37·8° C. remained within a narrow range, between 34.8°C. to 37°C. for the left testicle and 34.7°C. to 36.6°C. for the right testicle. 17. Artificial displacement of the testicle to close contact with the body resulted in an increased intra-testicular temperature of 2.5°C. and a decrease in the temperature of the scrotal area not overlying the testicle, of 6.0°C. and 3.2°C. The scrotal surface over the displaced testicle also increased considerably to 37.0°C. 18. The heat regulating mechanism of the scrotum is extraordinarily efficient in maintaining the testicular and scrotal surface-temperatures within a very narrow range at air-temperatures between 10°C. and 40°C. It is suggested that this efficiency is not purely physical, due to the action of air temperature on the contracted or relaxed scrotum. This suggestion is strengthened by the fact that scrotal areas I and II, in close contact with the testicle, behaved similarly but differently -to scrotal area III and the skin. It appears probable that vascular reaction accompanies scrotal contraction and relaxation. 19. The scrotal temperature reaction over that portion of the scrotum removed from close testicular contact, is extraordinary in that there was a very marked decrease in temperature to 28.2°C., i.e. 3.8°C. lower than air-temperature, and 8.8°C. lower than intra-testicular temperature (average for points 1 and 2). It is suggested that this reaction was an attempt by the temperature regulating mechanism of the scrotum to maintain the testicular temperature, which was raised by contact with the body , at the normal temperature for prevailing air-temperature.
A note on the results of an attempt to fertilise native goat-ewes with sheep-rams
(Pretoria : The Government Printer, 1941) Quinlan, John; Roux, L.L.; Van Aswegen, W.G.; De Lange, N.; Du Toit, P.J.
(1) Ten female native goats were mated to, or artificially inseminated with semen from a number of highly fertile sheep-rams during four breeding seasons. (2) There was great difficulty in obtaining fertilisation, but four of the ewes became pregnant; of these three aborted, while the foetus of the other died and underwent maceration. The pregnancy in each case terminated before the end of the normal gestation period. (3) The possibility of fertilisation occurring, followed by embryonic death and abortion, is not excluded. In fact it is supported by the irregular and long dioestrous periods experienced by the ewes. (4) Sexual activity was usually confined to the months January to August, but in a few cases oestrus appeared at irregular intervals throughout the year. (5) At death or slaughter, during the usual anoestrous season, seven of the ewes showed ovarian inactivity, two showed hydrometra and one showed foetal maceration.
The hydrogen-ion concentration of the vaginal secretion of merino sheep during oestrus, dioestrus, and pregnancy, with some remarks on its influence on sex-determination, and the influence of the vaginal temperature at the time of mating on conception
(Pretoria : The Government Printer, 1941) Quinlan, John; Myburgh, S.J.; De Vos, D.; Du Toit, P.J.
(1) The pH of the vaginal secretion of mature merino ewes, measured during oestrus, gave a mean value of 6·648, with a range of 5·85 to 7·40. During mid-dioestrus the mean value was 6·694, with a range of 6·00 to 7·60. During pregnancy the mean value was 6·272, with a range of 6·00 to 7·00. There are indications that there is a tendency to slightly increased acidity during oestrus and pregnancy. (2) There are indications that there is a slight tendency for male offspring to be associated with a pH approaching neutral or alkaline measurements. (3) The percentage fertility was higher with pH measurements below 7 (82·51 per cent.) than with those above 7 (73·18 per cent.). There are indications that an alkaline medium may be detrimental to the vitality of the spermatozoa in the vagina when pregnancy is used as an indicator. (4) Forced exercise increased the vaginal temperature of ewes when they are compared with ewes, kept under similar environmental conditions, which were allowed voluntary exercise. (5) The temperature of the vagina (within a range of 100·2°F. to 106·2°F.), at the time of mating or artificial insemination did not influence the sex of the lamb. (6) The temperature of the vagina, within a range of 100·2°F. to 106·2°F., did not make a significant difference in the resulting pregnancies in three groups of sheep with mean temperatures, at 1st and 2nd matings or artificial inseminations, of: (1) 103·286, 103·264, (2) 103 ·244, 103·096, and (3) 104·017, 104·108 (temperatures are recorded in °F.). (7) The gestation period, for 79 normal pregnancies in merino sheep, showed a range of 146 to 156 days, with an average of 151·4 days.
Studies on the photosensitisation of animals in South Africa. XI. The reaction of the sensitised Merino skin to radiation in different regions of the spectrum
(Pretoria : The Government Printer, 1941) Riemerschmid, G.; Quin, J.I.; Du Toit, P.J.
1. The effect of sunlight on sheep artificially photosensitised with eosin and phylloerythrin was investigated. Glass filters were used to ascertain whether any of those rays readily absorbed by these dye-stuffs produced skin reactions. Small square test areas on the back of photosensitised sheep were exposed under these filters to solar radiation for various lengths of time, up to six hours. 2. A spectral distribution curve was calculated for the solar radiation at Onderstepoort for an altitude of the sun of 65° and 35° respectively. When this spectral distribution curve was combined with the absorption spectrum of eosin and phylloerythrin the resulting curve delimitated those regions of the spectrum which might be expected to yield skin reactions in the photosensitised sheep. The results may be summarised as follows: (a) The skin of closely shorn, non-photosensitised, adult merino sheep, exposed to solar radiation for several hours showed only a light erythema which rapidly subsided without oedema formation. (b) Sheep photosensitised with phylloerythrin (dried leaves of the Lantana camara plant) and subsequently exposed to sunlight, showed reactions which increased in severity depending on the duration of exposure. (c) The reactions of the skin of sheep photosensitised with eosin, were strictly confined to those parts of the spectrum where eosin strongly absorbs radiation, namely from wavelength 540-460 mµ, i.e. in the green and blue part of the spectrum. (d) The phylloerythrin absorption is spread over a much wider area than that of eosin. The phylloerythrin shows three regions of absorption namely a single band from 654 to 626 mµ (orange), a triple band between 610 and 510 mµ (yellow and green) and high absorption below 460 mµ (blue, violet and ultraviolet). The filter experiments showed that reactions in the skin of sheep photosensitised with phylloerythrin were restricted to parts of the spectrum where radiation is absorbed by phylloerythrin, namely the region between 650 and 380 mµ, which includes practically all visible light.

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