1951 Onderstepoort Journal of Veterinary Research, Volume 25, Number 1 & 2, 1951
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Item The use of egg attenuated bluetongue virus in the production of a polyvalent vaccine for sheep. A. Propagation of the virus in sheep(Published by The Government Printer, Pretoria, South Africa., 1951) Alexander, R.A.; Haig, D.A.; Alexander, R.A.; Clark, R.; Sterne, M.; Louw, J.G.; Van der Reyden, D.; De Kock, V.E.(1) A brief description of Theiler's classical method of bluetongue vaccine production is given and various modifications introduced from time to time are recorded. (2) In an attempt to adapt the recognized technique to the routine mass production of a polyvalent vaccine using fully attenuated egg adapted (A) strains of virus three difficulties were encountered : (a) As a result of even a single passage through susceptible sheep the adapted (A) strains were transformed at least partially into apparently original or sheep strains (O) so that quantitative control could not be carried out in eggs. (b) During the course of change from the A to the pseudo-O phase at least some strains show a marked change in antigenic structure. (c) Since the majority of sheep infected with egg attenuated virus show no clinical reaction it is impossible to eliminate animals included by accident amongst the virus donors. In the final mixture specific antibodies in the serum of such immune sheep neutralize the virus propagated in the susceptible donors, thus making the vaccine inert. This has proved an insurmountable difficulty. (3) Though passage through sheep causes a change from the A to the pseudo-O type of virus there is no reversion to original virulence.Item A contribution to the cytology of the spleen: the Romanowsky-stained bovine spleen smear(Published by The Government Printer, Pretoria, South Africa., 1951) Jackson, Cecil; De Boom, H.P.A.; Alexander, R.A.; Clark, R.; Sterne, M.; Louw, J.G.; Van der Reyden, D.; De Kock, V.E.A. The essence of this work has been to provide a systematic description of the elements and an explanation of the chief artefacts of the bovine spleen smear together with an atlas-guide. Hence no general summary is possible. But attention should be drawn especially to the following points: (1) The most active phagocytosing cell of the bovine spleen is a lymphocyte, termed a a phagocytosing lymphocyte by us, and doubtlessly corresponding to the macrophage, clasmatocyte (smaller type), " splenocyte", and even perhaps the "monocyte" of some authors. (2) Phagocytosis in the spleen includes erythrocytes, leucocytes, and blood platelets. Thrombophagocytosis is a very extensive phenomenon in the spleen of bovines, only to be appreciated by the use of refined technique. (3) Monocytes are of infrequent occurrence. They are derived from reticulum cells, through an intermediate stage which may be spoken of as a monoblast; but not from lymphocytes. (4) Although ultimately in aged plasma cells distinction between the two types is impossible, plasma cells may be derived from reticulum cells and monocytes, as well as from lymphocytes. (5) The sinus-lining cells have a distinct morphology, especially in their nuclear characters and their content of iron-containing pigment "haemofuscin" at both poles of the nucleus. No evidence of phagocytic or cytogenic abilities could be demonstrated. (6) The Schweigger-Seidel sheath cells are described in smears and details of their morphology are provided. The view is advanced that they are of the same nature as reticulum cells as far as reticulin production, mobilisation and phagocytosis are concerned, although differing morphologically from them in the resting state. (7) The nature of certain puzzling epithelial-like elements in routine spleen smears was cleared up by the finding that they are mesothelial cells of the splenic serosa. B. Besides the cells already mentioned, the following elements are briefly described as they appear in the Giemsa-stained spleen smear: endothelial cells, smooth muscle cells, mast cells, eosinophils (their youthful appearance and the presence of Liebreich's alpha 1 granules are commented upon), neutrophils (mention has been made of their macrophagocytic activity), megakaryocytes, erythrocytes, as well as blood platelets, reticulin, collagen and elastic fibres, haemosiderin and "haemofuscin". C. The status and genesis of artefacts have been discussed. Theoretically a distinction can be drawn between artefacts produced by making and subsequent manipulation of preparations (exogenously produced artefacts), artefacts conditioned by states of senescence or degeneration of the cells (endogenously conditioned artefacts), and artefact-like appearances resulting from physiological processes; in practice this distinction is not always possible. The artefacts described include cellular distortion, cytoplasmic fragments and free cytoplasmic constituents, naked nuclei, distorted and smudged nuclei, various contaminants, stain deposit, etc. The effects of autolysis have also been mentioned. D. Problems of cell derivation and terminology have been discussed. E. In view of the phagocytic powers of lymphocytes and neutrophils and the inactivity of the sinus endothelium in this respect, a critique is offered on the R.E. system, and the proposal is put forward that the name be changed to "Phagocytic System".Item The South African biting midges of the genus Culicoides (Ceratopogonid., Dipt.)(Published by The Government Printer, Pretoria, South Africa., 1951) Fiedler, O.G.H.; Alexander, R.A.; Clark, R.; Sterne, M.; Louw, J.G.; Van der Reyden, D.; De Kock, V.E.Item The influence of nutritional level on verminosis in merino lambs(Published by The Government Printer, Pretoria, South Africa., 1951) Laurence, G.B.; Groenewald, J.W.; Quin, J.I.; Clark, R.; Ortlepp, R.J.; Bosman, S.W.; Alexander, R.A.; Clark, R.; Sterne, M.; Louw, J.G.; Van der Reyden, D.; De Kock, V.E.1. A mass mixed infestation of Haemonchus contortus and Oesophagostomum, columbianum larvae dosed to 7-8 month old merino lambs kept on two different planes of nutrition caused a peracute fatal verminosis in all the infested animals. 2. A similar infestation when dosed to 10-11 month old lambs under identical conditions caused a chronic verminosis. In this case the effect of nutrition on the response of the animals to verminosis was clearly demonstrated. 3. This finding demonstrates the greater susceptibility of young lambs to worm infestation, regardless of their diet, and emphasises the necessity of preventing mass infestation in young lambs under all conditions. 4. In the second experiment it was shown that an increase of the maize ration by 300 gm. a day caused a marked superiority in worm infested sheep as regards all of the following factors : - Body weight, appetite for roughage, haemoglobin level, fleece weight and wool fibre thickness. 5. In all the above respects the worm infested sheep receiving 400 gm. of maize per day were superior to the non-infested sheep receiving only 100 gm. of maize per day. 6. The pathological findings in cases of acute verminosis are described and the immediate cause of death was found to be acute, pulmonary oedema. 7. Phenothiazine was found to be superior to either tetrachlorethylene emulsion or copper tartrate and copper arsenate mixture as a vermifuge in that it appeared not only to kill all wire worm present but also to cause removal of the black-stained ingesta from the alimentary tract. It also appeared to promote normal bileflow. 8. The experiment clearly demonstrates the beneficial effects of a higher maize intake on the response of sheep to verminosis.Item The oestrous cycle of the mare when maintained under stabled conditions with restricted exercise at Onderstepoort(Published by The Government Printer, Pretoria, South Africa., 1951) Quinlan, J.; Steyn, H.P.; Van Rensburg, S.W.J.; Alexander, R.A.; Clark, R.; Sterne, M.; Louw, J.G.; Van der Reyden, D.; De Kock, V.E.(1) Observations were carried out on the oestrous cycle of 30 mares from January, 1944, to June, 1946. (2) The mares were stabled at night and ran out in a small paddock during the day. They were never let out to grazing but received a uniform ration throughout the year with the exception that green feed was given during the summer months but not during winter. (3) They were tested for oestrus every day and mares that showed symptoms of oestrus were mated. (4) The results revealed that the oestrous cycle in these mares was not seasonal, but that it continued throughout the year in the majority of animals. (5) There was, however, a noteworthy decline in the percentage of mares that showed oestrus in April and May. (6) The cycles were very irregular and varied in length from 6 days to 113 days. The irregularities occurred throughout the year, but were most pronounced during the months of February to July. The average length of the cycles for this period was 35•9 days as against 23•8 days for the remaining six months of the year. The average length of the oestrous cycles for the whole year was 29•9 days. (7) The increase in the average length of the cycles for February to July is largely due to the fact that a number of mares went into varying periods of anoestrus during these months. This also accounts for the abnormal length of the average for the cycle throughout the year. (8) There were 17 periods of anoestrus varying in duration from 46 to 113 days. With one exception all these occurred during the first seven months of the year. (9) The average duration of oestrus was found to be 6•93 days. Oestrus was shorter (average of 5•7 days) in the first half of the year than in the second half when the mean was 8•03 days. In the latter it was highest during the early months of breeding (July to October). (10) The oestrous period was found to be as variable as the oestrous cycle. The shortest period was 1 day and the longest 55 days. (11) The months of April, May, June and July were found to be barren in so far as none of the mares that were mated then became pregnant. It is concluded that the 50 oestrous periods that were shown during these months were not accompanied by ovulation. (12) Fecundity was low during the first three months of the year. Then ceased for four months from April to July and commenced again in August. The highest percentage of pregnancies (55•6) was obtained from service in November. (13) Nutritional factors are considered to be responsible for irregularities in the oestrous cycle and for the low fertility. (14) Most of the pregnancies resulted from mating during oestrous lasting from 3 to 8 days. (15) It is doubtful whether the duration of oestrus influences fertility. The latter depends on service at the time of ovulation. This is also variable and may even occur 19 or 20 days after the commencement of oestrus.Item Studies on the alimentary tract of the merino sheep in South Africa. XXIII. The effect of supplementing poor quality grass hay with molasses and nitrogenous salts(Published by The Government Printer, Pretoria, South Africa., 1951) Clark, R.; Quin, J.I.; Alexander, R.A.; Clark, R.; Sterne, M.; Louw, J.G.; Van der Reyden, D.; De Kock, V.E.1. In a series of three experiments it has been shown that the supplementation of poor quality grass hay with either urea or sodium nitrate, in conjunction with molasses resulted in increased appetite and improved maintenance of body weight. 2. These beneficial effects were not only due to the extra nutriments derived from the supplements but also to an acceleration of cellulose digestion allowing of a greater utilisation of the basic hay. 3. Although the rate of cellulose digestion was accelerated the percentage of cellulose digested was not influenced. 4. The feeding of 200 gm. of lucerne hay per day also increased the rate of cellulose digestion resulting in an increased consumption of grass hay. 5. Indications that the presence of ammonia radicle is deleterious to the activity of the ruminal flora will have to be studied further. The possibility of using nitrates to supplement the rations of ruminants will also have to be explored.Item Studies on the alimentary tract of the merino sheep in South Africa. XXII. The effect of the pH of the ruminal contents on ruminal motility(Published by The Government Printer, Pretoria, South Africa., 1951) Clark, R.; Lombard, W.A.; Alexander, R.A.; Clark, R.; Sterne, M.; Louw, J.G.; Van der Reyden, D.; De Kock, V.E.1. It has been shown that the administration of alkali (sodium carbonate or sodium hydroxide) into the rumen causes ruminal paresis if the pH exceeds approximately 7•5. 2. Ruminal paresis can also be caused by the intravenous injection of alkali (sodium hydroxide or ammonia) indicating that the paresis associated with alkalinity of the ruminal ingesta is of central origin. 3. No corresponding effect could be demonstrated following the dosing or injection of acid. 4. The paretic ruminal musculature is still capable of normal contraction as shown by the reaction to feeding and the response to carbamylcholine. 5. The possible significance of alkalinity of the ingesta in the aetiology of ruminal stasis is discussed.Item Studies on the alimentary tract of the merino sheep in South Africa. XXI. The toxicity of urea to sheep under different conditions(Published by The Government Printer, Pretoria, South Africa., 1951) Clark, R.; Oyaert, W.; Quin, J.I.; Alexander, R.A.; Clark, R.; Sterne, M.; Louw, J.G.; Van der Reyden, D.; De Kock, V.E.The dosing of urea into the rumen of sheep caused acute intoxication characterised by atony of the rumen, muscular spasms and sudden death due to circulatory failure. The toxicity of urea was found to depend on the activity of the ruminal flora, as determined by the basic diet, and the presence of available carbohydrate. Toxic symptoms after dosing urea were associated with the formation of ammonia and a high pH of the ruminal contents. They could be prevented or alleviated by the administration of acid.Item Studies on the alimentary tract of the merino sheep in South Africa. XX. The failure of the rumen musculature to respond to carbamylcholine chloride when paralysed by potassium cyanide(Published by The Government Printer, Pretoria, South Africa., 1951) Clark, R.; Alexander, R.A.; Clark, R.; Sterne, M.; Louw, J.G.; Van der Reyden, D.; De Kock, V.E.1. It was found that acetylcholine did not restore motility to the isolated rabbit duodenal strip inhibited by prussic acid. 2. Similarly ruminal paresis induced by, prussic acid could not be successfully treated with carbamylcholine chloride In fact such treatment caused an increase in the severity and duration of the ruminal stasis. 3. Carbamylcholine and prussic acid combine in causing respiratory and circulatory failure.Item Studies on the alimentary tract of the merino sheep in South Africa. XIX. The influence of sulphanilamide on the activity of the ruminal flora of sheep and cattle(Published by The Government Printer, Pretoria, South Africa., 1951) Oyaert, W.; Quin, J.I.; Clark, R.; Alexander, R.A.; Clark, R.; Sterne, M.; Louw, J.G.; Van der Reyden, D.; De Kock, V.E.(1) It has been shown that therapeutic doses of sulphanilamide depress cellulose digestion and appetite in ruminants. (2) The fermentation of sugar and gas formation are also suppressed but only by higher concentrations. (3) The absorption of sulphanilamide after intra-ruminal dosing is very slow and effective blood concentrations are not attained with recognised therapeutic dosage. (4) The absorption of sulphanilamide is further retarded by paralysis of the rumen induced by atropin. (5) These findings raise the question as to the advisability of dosing sulphonamides to ruminants in view of their deleterious effects on cellulose digestion and appetite and the low blood concentration of the drug achieved by dosing.Item Studies on the alimentary tract of the merino sheep in South Africa. XVIII. The effect of fasting on the activity of the ruminal flora of sheep and cattle(Published by The Government Printer, Pretoria, South Africa., 1951) Quin, J.I.; Oyaert, W.; Clark, R.; Alexander, R.A.; Clark, R.; Sterne, M.; Louw, J.G.; Van der Reyden, D.; De Kock, V.E.1. The effects of starvation on the consistence of the ruminal ingesta and the activity of the ruminal flora have been studied. 2. The ruminal contents were found to become progressively more watery during starvation although there was still a large volume present even after 96 hours without food. 3. Both the fermentation of sugar and the digestion of cellulose were markedly depressed after 48 hours starvation. 4. On a low protein diet of grass hay the appetite returned to normal immediately after starvation but on a higher protein diet of lucerne hay the consumption after starvation was low and only returned to normal after 3 to 5 days. There was evidence to show that the sheep regulated their protein intake in accordance with the adaptation of the ruminal flora. This did not appear to apply to the same extent to cattle.Item The Brucella ring test for milk of individual cows and its value for determining their status of infection(Published by The Government Printer, Pretoria, South Africa., 1951) Van Drimmelen, G.C.; Alexander, R.A.; Clark, R.; Sterne, M.; Louw, J.G.; Van der Reyden, D.; De Kock, V.E.1. A technique is described whereby the Brucella Ring Test for milk can usefully be applied to individual cattle. 2. Results are reported which suggest that the Ring Test on individual animals may give a very useful indication of the real status of infection in a cow (except when she was vaccinated within three to four months previously; or infected within a few weeks previously). 3. Advantage of a test which requires little technical skill and of which the results are available within an hour are pointed out. 4. The test previously utilised for the determination of infection in cattle herds are briefly reviewed. 5. Views on the mechanism of the Ring Test Reaction and its relation to antibody production in the udder are recorded.Item A photometric method for quantitative paper partition chromatography of amino acids(Published by The Government Printer, Pretoria, South Africa., 1951) Polson, A.; Van Rooy, P.J.; Marais, E.J.; Alexander, R.A.; Clark, R.; Sterne, M.; Louw, J.G.; Van der Reyden, D.; De Kock, V.E.Due to the difficulties involved in the visual estimation of amino acids in protein hydrolysates from serial dilutions on chromatograms a very simple photoelectric method was devised to facilitate the accurate estimation of amino acid concentration. Sources of errors which must be avoided are temperature fluctuations of the chromatographic tank, non-uniform application of ninhydrin to the filter paper, too high amino acid concentrations and discolorations of the filter paper by organic solvents. The method was applied to the analysis of silk fibroin and values were obtained which agreed well with those determined by previous workers.Item Studies in demyelinating diseases of sheep associated with copper deficiency. I. "Lamkruis," a demyelinating disease of lambs occurring in South Africa. II. A biochemical investigation on the incidence of " Lamkruis " in lambs in the Saldanha Bay, Vredenburg, and St. Helena Bay environs. III. Experimental studies, treatment and control measures(Published by The Government Printer, Pretoria, South Africa., 1951) Schulz, K.C.A.; Van der Merwe, P.K.; Van Rensburg, P.J.J.; Swart, J.S.; Alexander, R.A.; Clark, R.; Sterne, M.; Louw, J.G.; Van der Reyden, D.; De Kock, V.E.It cannot be claimed that the observations recorded have led to specific information as to the cause of the disease known as "lamkruis", yet valuable information has been obtained which makes it clear that the factors originally suspected, i.e. phosphorus and copper deficiency, can now be disregarded as the primary aetiologic factors. An ataxia of lambs called "lamkruis" or "litsiekte" was found to occur on the south and west coast of South Africa, mostly on the calcareous soils of recent origin but also on soils of partly granitic origin. Clinically it is a non-febrile disease characterized by a swaying gait in the hindquarters. When the lambs are driven they stumble easily and fall on to their sides. The striking pathologic feature is destruction of the myelin in the nervous system, and, in extreme cases, symmetrical areas of softening or cavity formation occur in both cerebral hemispheres. The white brain substance is principally affected. Cavity formation is extremely rare in the spinal cord. Lamkruis is probably identical with other demyelinating diseases affecting lambs in various parts of the world, for instance, enzootic ataxia or ataxia of young lambs in Australia and New Zealand, " swayback" or "singback", or "warfa" in England and Scotland, and "renguera" in Peru, Patagonia and the Argentine. "Lamkruis" as we know it in this country only develops in the progeny of ewes subjected to a pasture of a "low" copper content. Without a single exception the liver copper value of both ewes and their Jambs was of a low order. There is evidence, however, that a low copper content of the liver is not pathognomonic for Lamkruis. Presumably, therefore, the ataxia is not necessarily caused primarily by a copper deficiency. The ataxia is, therefore, probably not due to a copper deficiency alone. In this respect it differs from enzootic ataxia or ataxia of young lambs and is similar to swayback and renguera. It is assumed that copper may only be a link of a chain of contributory causes. The process of demyelination cannot be ascribed to a single factor such as a copper deficiency. It has been shown that, although the common lesion-demyelination is an anatomical entity, its aetiology need not necessarily be identical in each case. The view is expressed that in the case of " lamkruis" the lesions must be correlated with a circulatory disturbance and / or a possible defective tissue anabolism brought about by a deficiency of circulating copper. The bilateral symmetry of the lesions suggests a systemic involvement. The beneficial effect of administering copper salts to pregnant ewes in reducing or preventing the appearance of "lamkruis" in their progeny has been demonstrated. In this respect our findings are in close agreement with those of the other demyelinating diseases of lambs. l\It cannot be claimed, however, that the administration of copper salt has a curative effect on diseased lambs. The administration of copper salts to affected lambs may seem to have a curative effect in some cases. It should be remembered however that a number of animals may recover without any treatment at all. Apparent or total recovery, probably depends on the extent and degree of the lesion and the affected structure. Presumably in "lamkruis" the demyelination is due to a patho-physiologic process and the beneficial effects of copper may be ascribed to its physiologic or therapeutic properties rather than to its direct association with myelination. The ataxia seen in "lamkruis" is presumably not associated with the lesions in the cerebral hemispheres, since there was no relationship between the severity of the clinical symptoms and the extent of the lesions. The possibility that the ataxia is associated with alterations in the cerebellum or brain-stem or both, must be considered. The high concentration of iron and the low copper level in the livers of adult sheep and lambs on "affected" properties indicate a disturbance in the iron metabolism and may possibly be due to the absence from the food supply of some factor (cobalt) necessary for its utilization as is the case in enzootic marasmus. Presumably most of this iron is immobilized and stored in the organs, since only a very small amount is demonstrable in sections stained with •Berliner Blue and this does not occur principally in the form of haemosiderin. The haemoglobin values for both ewes and lambs may reasonably be considered to be of a low order. However, the magnitude of the values obtained is not such that one is justified in stating that haemoglobin synthesis and haemopoiesis have seriously been affected, since a very low blood copper level (less than 0•1 p.p.m.) apparently does not interfere with normal haemopoiesis. Evidence has been produced suggesting that a gradual rehabilitation to a normal iron-copper metabolism may take place but that the intra-uterine injury to the central nervous system may be permanent. It seems that the biochemical processes concerned in the copper and iron metabolism of the body may proceed normally, in spite of a marked depletion of the copper stores of the ewes and the developing lamb, and the condition may further be complicated by a significant deviation of the iron stores of the body from the normal. Based on the present evidence we wish to emphasise a post-natal as well as a pre-natal onset for " lamkruis" and related diseases. Possibly all cases developing within three months after birth may be looked upon as "delayed" pre-natal cases, whereas those occurring later are most likely post-natal. Although the end results may be identical, the pathogenesis in the various forms may differ in several respects. A reduced phosphorus content was demonstrated in the soil the vegetation, the blood and tissues of stock grazing on the " Strandveld" (Bredasdorp, Riversdale and Swellendam areas) and this was reflected in softness and fragility of the bones of the animals concerned, whereas no evidence of an apparent phosphorus deficiency was obtained in the vicinity of Saldanha Bay and Vredenburg. Phosphorus deficiency is probably a contributory factor of the disease called "heupsiekte" in cattle and that which was mistakenly termed " lamkruis " in older sheep by former investigators. The disease described by us has nothing in common with the previously mentioned condition. In some of these coastal areas several diseases, such as "duinesiekte" of sheep and young cattle, paratyphoid of calves, and " broken wind" in draught animals (called “ruksiekte" or "benoudebors") or "bighead" (osteofibrosis) in horses, may be very prevalent. The possibility of greater susceptibility of animals to diseases under conditions prevailing in these coastal regions is a problem that requires further investigation. Other diseases, for instance "slapsiekte" of lambs and donkeys, affections of lambs and goats due to Coenurus cerebralis, and "Malkop" occurring more inland and characterized by nervous symptoms, have been described. In addition some demyelinating diseases affecting man and presumably not associated with a copper deficiency have been mentioned. Evidence has been thereby produced indicating that diseases with similar clinical symptoms and morbid changes need not necessarily have the same aetiology. However, there may be some common factor responsible for their similarity. " Lamkruis " is not related to imperfect osteogenesis nor to a degeneration of the musculature as that seen in " white muscle" disease. The alterations in the central nervous system are not those of aplasia of the white substance of the brain nor of an inflammatory nature, but must be ascribed to an encephalomyelopathy or a diffuse leucoencephalopathy without sclerosis. The process in cavity formation appears to be that of autolysis occurring intra vitam. It is characterized by a scarcity of fat and "gitter cells". In this respect "lamkruis" differs significantly from Schilder's Disease, but is in close agreement with diffuse leucoencephalopathy of man (Josephy and Lichtenstein, 1943). Post mortem changes can be eliminated since the specimens were placed into formalin within a few minutes after slaughtering of the animals. Deficiencies of copper, phosphorus and vitamins may be excluded as primary causes, but they probably act as contributory factors. Apparently poisonous plants and fungi do not play a role in the aetiology of this disease. As the disease may occur intra-uterine it is essential that the placental circulation (maternal and foetal) and the chemical changes occurring in the foetal brain should receive more attention than in the past. Progress in elucidating the pathogenesis of "Jamkruis " and other related diseases may be expected, if the significance of these two factors will be fully appreciated. It is well-known that several demyelinating diseases occur in man and that demyelination can be produced experimentally by a number of variable factors and not necessarily by a copper deficiency. Our cases, as well as those mentioned in the literature, point to the necessity for careful neurologic study in all cases of "lamkruis " and similar conditions. The distribution and character of cerebral lesions in " lamkruis " are indicative of circulatory disturbances and the resultant alterations in the affected localities. More attention should be given to less pronounced changes, especially in the cerebellum, brain-stem and other organs, for instance the adrenal.Item Fowl-pox vaccination in South Africa with egg-propagated fowl and pigeon-pox viruses(Published by The Government Printer, Pretoria, South Africa., 1951) Haig, D.A.; Alexander, R.A.; Clark, R.; Sterne, M.; Louw, J.G.; Van der Reyden, D.; De Kock, V.E.1. Fowl-pox as it occurs in the Union of South Africa is reviewed briefly together with relevant literature on the methods of immunization. 2. In South Africa until recently vaccine prepared from virus propagated on pigeons has been used for immunization of poultry. The reasons for abandoning this vaccine are discussed. 3. The technique of propagating fowl- and pigeon-pox virus m eggs is discussed, attention being paid to :- (a) The influence of temperature of incubation; (b) The time allowed for multiplication; (c) The distribution of virus in the eggs; (d) The virus titre of infected membranes; (e) The isolation of pigeon-pox virus strains. 4. The preparation of fowl- and pigeon-pox virus vaccine is described with particular reference to : (a) Potency of the vaccine and its estimation; (b) The keeping quality; (c) The correlation between infectivity for egg and for chickens.