1947 Onderstepoort Journal of Veterinary Science and Animal Industry, Volume 21, Number 2, 1947
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Item Meat studies. No. 1. Post-natal growth and development of muscle, as exemplified by the gastrocnemius and psoas muscles of the rabbit(Pretoria : The Government Printer, 1947) Meara, P.J.; Du Toit, P.J.Attention is directed to the paucity of information regarding the morphological growth and development of muscle, particularly in connection with the microscopical elements comprising muscle. Such knowledge is of value, not only in affording a basis for studying meat quality in different species of domestic animals, but also in understanding the principles underlying the function of different muscles. In a preliminary study, statistical methods were employed in order to ascertain suitability of sampling and measuring muscle bundles and muscle fibres. For sampling the bundle length of a muscle, a selection of ten measurements gives a sufficiently reliable mean. For sampling the diameter of muscle fibres, a selection of one hundred measurements affords a sufficiently reliable mean. Variable results are obtained when a measure of fibre diameter is calculated from cross-sections of muscle, probably due to the difficulty of cutting sections at right angles to the line of the fibres. Measurement of the cross-diameter of short lengths of muscle fibres yields more reliable results, and the values obtained are greater than those obtained by measuring fibre diameter in cross-sections. For calculating the texture of a muscle, a selection of twenty bundles provides a fair estimate of the number of fibres comprising the individual muscle bundle. With the object of establishing the general principles of morphological development during post-natal life, the relative changes were studied in the tissues and anatomical units of M. Gastrocnemius medialis and M. Psoas major, in a series of male rabbits killed at intervals from birth to fourteen months of age. Throughout this study, the quantitative data were subjected to statistical analysis. Qualitative changes were not considered. The work is to be regarded as a preliminary investigation, with the purpose of drawing attention to the main principles involved in the growth of the muscles studied. Both muscles undergo extensive enlargement during the growth of the rabbit. Relative to the Psoas muscle, M. Gastrocnemius makes a greater proportion of its growth in mass early in life. Although no important differences were revealed in the mechanism of lengthening of these muscles, there is a striking difference in the manner whereby the individual muscle bundles contribute to this length increase. Whereas the Psoas muscle lengthens by virtue of a persistent increase in the length of its component bundles, Gastrocnemius bundles do not lengthen after the first two months of life. During the remainder of the lifetime of the rabbit, they do not contribute to the appreciable degree of lengthening which is still manifested by the Gastrocnemius muscle. Because of the oblique position of the bundles, thickening of these bundles appears to be the principal factor promoting this increase in length of the muscle. A change in the relative position of these bundles within the Gastrocnemius muscle tends to increase the depth of the muscle. Both muscles vary appreciably in form. M. Gastrocnemius is short, with a pronounced belly, and is more or less uniformly deep. M. Psoas is long, with a less marked belly formation, and becomes progressively thicker along its length from origin to insertion. In the absence of information regarding the working of these muscles, the advantages of the respective variations in form in promoting muscular efficiency cannot be discussed. Contrary to expectation, the muscles do not widen or deepen during a later stage of the lifetime of the animal than they increase in length. Within M. Gastrocnemius, the individual bundles show well-defined differential length relationships. In the young rabbit, the bundles show a progressive increase in length along the length of the muscle from its origin to its insertion. In the older rabbit, the bundles are shorter a little distance beyond the muscle origin than at the origin itself, then exhibit a similar increase in length along the muscle to its insertion. The change from one system to the other occurs between 320-480 gm. live-weight, at about 3-4 weeks of age. In both muscles the bundles continue to thicken throughout the period of growth. Although there is only a slight difference in bundle thickness in the new-born rabbit, Gastrocnemius bundles subsequently thicken at a greater rate and become increasingly thicker than the Psoas bundles, as the animal becomes older. Hence M. Gastrocnemius assumes a coarse texture relative to the Psoas muscle. The bundles comprising the Psoas muscle contain a larger number of individual fibres than the Gastrocnemius bundles. However, as regards muscle texture, this numerical superiority is more than offset by the greater fineness of the fibre in the Psoas bundles. No evidence was obtained of any decrease in the number of muscle fibres during the post-natal life. Hence, the enlargement in form and the increasing weight of the muscles must be considered to be due mainly to an increase in the size of the existing muscle fibres. Length of Gastrocnemius muscle fibre is an extremely early developing character. In the Psoas muscle the fibres continue to lengthen throughout the period of growth. This increase in the length of Psoas fibres is largely responsible for the increase in bulk of the muscle. Within each muscle, the fibres show a well-defined thickness relationship. In M. Gastrocnemius, the fibres at birth are thinner in mid-muscle than at both ends of the muscle. At all succeeding stages the Gastrocnemius fibres are thinnest near the origin, then become progressively thicker along the muscle to a point near the muscle insertion. By contrast, the Psoas fibres are at all stages thinnest in the middle of the muscle. Presumably these differences in the relative size of the contractile units are dictated by functional considerations. The Gastrocnemius fibres thicken to a greater degree and become much thicker than the fibres in M. Psoas. Because of the early cessation of length growth in the Gastrocnemius muscle fibre, this thickening of the component fibres largely accounts for the increase in the bulk of M. Gastrocnemius. Any application of the data to a different species of animal, or to different muscles, will naturally require caution. However, the general principles for the two basically different classes of muscle studied are probably similar in allied types of a wide variety of muscle. The essential structural difference of these two types is the direction of the muscle fibres. In M. Gastrocnemius, of pinnate structure, the short muscle fibres join the tendon at an acute angle, whereas in the Psoas muscle, the fibres are characterised by their parallel arrangement from end to end of the muscle. For a large bulk of muscle, the general conclusions may be of value in providing a basis for further study of muscle belonging to either of these types. No mention has been made whether the data collected for the various measurements obey Huxley's allometric law. This aspect of the work is undergoing investigation, and will be presented in a future publication. At this stage, it can be stated that a straight-line relationship in logs. can be fitted to all the data by the method of least squares (i.e. allometric growth), excepting Gastrocnemius weight, Gastrocnemius depth, and muscle length and bundle length for both muscles. However, graphical analysis by means o£ confidence-regions eliminates in addition a number of the measurements showing a straight-line relationship in logs. by the least squares method. Thus, the method of curve-fitting completely satisfying the confidence region criterion shows that M. Gastrocnemius grows in allometric manner only for fibre diameter. Similar treatment for the Psoas muscle leaves only weight, width, and depth of muscle in the category of measurements which obey Huxley's law. Until it is possible to elaborate the reasons for the discrepancies, as well as the dissimilarities in the muscles studied, no useful purpose can be served by discussion or comparison.Item The effect of diet and body condition on the heat regulating system of the merino sheep(Pretoria : The Government Printer, 1947) Clark, R.; Quin, J.I.; Du Toit, P.J.1. It is clearly shown that the diet and general body condition of sheep markedly influenced their heat-regulating mechanism. 2. The maintenance of the body temperature of thin sheep in a cold environment was found to be closely associated with the calorific value of the diet at the time of exposure. 3. Moderately conditioned sheep maintained their body temperature when exposed to cold for a period of 10 days after being placed on an inadequate ration. 4. The control of temperature in a hot environment was found to depend largely on general body condition. 5. When the sheep were exposed to heat the following observations were made: (a) Thin sheep on a poor diet showed a suppressed panting reflex and an excessive rise in body temperature. (b) Thin sheep on a good diet showed a normal panting reflex but also an excessive rise in rectal temperature. This anomaly cannot as yet be fully explained. The ability to control the body temperature returned when the general body condition improved. 6. Contrary to expectation, continued poor feeding of sheep in conjunction with repeated exposure to cold failed to cause any clinical disturbance either in digestion or in the normal appetite of such animals. The effect of this treatment on the heat regulating system of the body, however, was both clear and pronounced.Item Ticks in the South African Zoological Survey collection. Part VI. Little known African rhipicephalids(Pretoria : The Government Printer, 1947) Theiler, Gertrud; Du Toit, P.J.1. Omitting unessentials, the descriptions of various little known Rhipicephalids and their geographical distribution have been republished. 2. The descriptions of R. distinctus, R. masseyi, R. theileri, R. tricuspis, R. simpsoni, R. supertritus are brought up to date. The nymphs of R. masseyi, R. tricuspis, R. distinctus and the larva of R. tricuspis are described for the first time. 3. R. falcatus and R. tricuspis are shown to be valid species. 4. R. attenuatus is sunk as synonymous with R. masseyi; R. cuneatus as R. ziemanni; R . lunulatus and R. glyphis as R. tricuspis; R. schwetzi as R. dux 5. Donitz' supposition that the occurrence for R. follis is "domestic stock, South Africa", is confirmed with reservations. 6. A list of the commoner African Rhipicephalids, whose descriptions are not included in this article, is given.Item Subject index(Pretoria : The Government Printer, 1947) Anonymous; Du Toit, P.J.Item Author index(Pretoria : The Government Printer, 1947) Anonymous; Du Toit, P.J.Item Meat studies no. 2 : toughness of meat(Pretoria : The Government Printer, 1947) Meara, P.J.; Du Toit, P.J.Qualities such as flavour, texture, juiciness, colour, and aroma contribute to the appreciation of meat. However, most people agree that tender meat is good meat. Toughness makes for unpalatability, or even inedibility for a section of the population. Agreement has not been reached regarding the nature of toughness, although the three constituents of meat - muscle fibres, connective tissue, and fat - must each play a role. Evidence is still inconclusive as to the exact relationship of the various factors contributing to toughness. A tasting panel may be formed to determine the final quality of the meat. Here selected persons taste a number of meat samples, and grade each sample on a scale of points for each of its properties (tenderness, texture, flavour, etc.). According to the score averaged for specific properties the samples can be rated, in order from best to poorest. In addition, various mechanical penetrating or cutting devices may be used to grade meat. Owing to the difficulty of establishing an efficient tasting panel these objective methods of measuring tenderness have many advantages. On the other hand, it is almost impossible to imitate the complex cutting and grinding action performed by the teeth, so that these instruments are not entirely reliable in interpreting human taste preferences.Item Notes on the thiocyanate iron reaction : a modified procedure for the quantitative determination of iron in biological materials(Pretoria : The Government Printer, 1947) Truter, G.J.; Du Toit, P.J.1. A modified procedure of the thiocyanate method for the micro-determination of iron in biological materials is described. 2. Evidence is presented to show its efficiency in the presence of moderate quantities of copper and relatively large concentrations of phosphate and calcium. 3. Hydrochloric or sulphuric acid is preferable to nitric acid, which should rather be avoided. 4. For colour stability it is essential to avoid recovered iso-amyl alcohol previously used for either iron or copper determinations. 5. A detailed description of a wet combustion procedure is given. 6. Some data on the iron and copper contents of tissues are given. 7. It can be concluded that the proposed method not only satisfies the need for a time-saving and simple procedure, but also conforms to the requirements for accuracy and reliability, if the necessary precautionary measures are taken.Item The supplementary effect between the proteins of a heat-treated soybean meal ("Soma Meal") and a South African strain of yellow maize seed ("Eksteen")(Pretoria : The Government Printer, 1947) Myburgh, S.J.; Du Toit, P.J.1. The proteins of an improved yellow maize strain popular in South Africa and that of a heat-treated soybean meal, supplemented each other to a small extent. 2. There was no determinable difference in the digestion or metabolism of the protein, when either the Hubbel or the Hawk and Oser Salt Mixtures were used in the rations with identical proteins.Item Studies on immunity in heartwater(Pretoria : The Government Printer, 1947) Neitz, W.O.; Alexander, R.A.; Adelaar, T.F.; Du Toit, P.J.1. It has been confirmed that the immunity in sheep following recovery from infection comprises a short period of premunition, followed by a period of gradually decreasing sterile immunity. 2. Infection during the period of sterile immunity again initiates the cycle premunition, sterile immunity. 3. Circulating virus is detectable in the peripheral circulation of immune sheep following reinfection, whether a demonstrable reaction is produced or not. 4. Up to a period of four years after recovery - the limit of the experiment - the residual immunity is sufficient to protect against fatal infection in sheep under laboratory conditions. 5. The significance of these findings and their relation to the problem of the control of heartwater are discussed.Item The attenuation of bluetongue virus by serial passage through fertile eggs(Pretoria : The Government Printer, 1947) Alexander, R.A.; Haig, D.A.; Adelaar, T.F.; Du Toit, P.J.1. A strain of virus (University Farm strain) was adapted to propagation in the developing chick embryo by incubation of infected eggs containing 8 day embryos at 33.6°C. but not at 32.1°C., 35.0°C. or 38.2°C. 2. After 3 serial passages at 33.6°C. it was possible to continue propagation at 32.1°C. and 35.0°C. but not at 38.2°C. 3. Using death of the embryos as an index of multiplication of egg-adapted virus there was little difference in the results obtained from incubation at 32.1°C. or 33.6°C. except that multiplication was slightly retarded at the lower temperature. At 35.0°C. the number of survivors beyond the 4th day of incubation was significantly increased. 4. There was little variation in the titre of emulsions produced from dead embryos at either of the temperatures after adaptation to eggs by serial passage. 5. The highest titre emulsions (not less than 10⁻⁵) together with the highest death rate on the 3rd day were produced from eggs incubated for 24 hours at 35.0°C. and then transferred to 32.1°C. 6. The virulent strain of virus was attenuated by serial egg to egg passage. At 32.1°C. attenuation took place rapidly after approximately 20 passages, at 33.6°C. at approximately the same rate, but at 35.0°C. it was delayed until about the 100th subculture. 7. Whether the attenuated virus produces a clinical reaction or not a solid immunity is produced against the homologous strain of virus. 8. The application of the results to the production of large quantities of vaccine for the mass immunization of sheep in the field is discussed.