Royal College of Physicians, Edinburgh.)

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1 ON THE RELATIONSHIP OF THE THYMUS TO THE SEXUAL ORGANS'. 1. The Influence of Castration on the Thymus. By JAMES HENDERSON, M.R.C.V.S. (Three Figures in Text.) (From the Laboratory of the Royal College of Physicians, Edinburgh.) IN their paper on the Physiology of the Thymus2 Noiel Paton and Goodall point out that in guinea-pigs the thymus continues to grow till the sexual organs become active, and that only after this does atrophy occur. They also refer to the observations of Friedleben which indicate that in the human subject the thymus increases in size till the fourteenth year and that atrophy is not marked until the twenty-fifth year. There thus seems to be some evidence of a relationship between the thymus and the sexual organs. It is a fact, well known to those engaged at abattoirs, that the thymus persists for a longer time and in greater volume in castrated animals than in those which are entire, but I ami not aware of any series of accurate observations on this subject, and at the instigation of Dr Noel Paton I undertook the following investigation on the influence of castration on the thymus, in the case of cattle killed as beeves in the Edinburgh abattoir. Cattle are preeminently suitable animals for the purposes of observation in this connection, first, because they are castrated at an early age between one and three months, and second, because they are slaughtered in large numbers before they reach maturity. Permanent dentition is completed at about four and a half years, and as the reproductive function is in action long before that period in the case of bulls and heifers, its effect upon the development of the thymus can be well observed. To obtain statistics the services of a reliable man whose business it is to kill and dress cattle for the market were engaged. He was furnished 1 The expenses of these observations were defrayed from the grant made by Mr Francis Mason for Investigations on the Ductless Glands. 2 This Journal, xxxi. p

2 THYMUS AND SEXUAL ORGANS. with a spring balance, the accuracy of which was previously tested. The two portions of the thymus (one from the lower part of the neck and the other from the anterior part of the thorax) were weighed, the small amount of fat adhering being estimated and deducted. In order to minimise error from this source several glands were entirely stripped of fat and the latter was in each case weighed to furnish a basis for such deduction. At the fat stock sales the living animal is weighed in presence of the buyers anid sold by live weight, and these sale weights were used for the purposes of this investigation. The age of the animals was judged by the number of permanent incisors erupted, the numbers being recorded with the weights. No record was kept of any animal having eight permanent incisors in wear because of the possibility of its being more than four years old. Six permanent incisors was the limit given so that it is practically certain that no cattle tested were more than three and a half years old. In judging the age of cattle by the development of the incisor teeth, some latitude must be allowed, as tardy or rapid dental development depends largely upon breed, kind of food and condition. The number of cattle tested was 114, of which 52 were oxen, 32 were bulls and 30 were heifers. The individual weights are given in the Appendix, and Table I, showing the average results, and Fig. 1, constructed from Table I, bring out the marked difference between the thytnus in the normal and the castrated aninmal. TABLE I. Oxen. Weight of th mus in No. or Weight in Weight of grs. per 100 kilos. of Age animals kilogrammes thymus in grs. body-weight 9-15 months ,, j years k,, Heifers months ;, j years , Bulls months ,, years ,,

3 224 J. HENDER1SON. In. actual weight of thymus those averages show in all three classes of cattle considerable irregularity at the ages recorded. It is very clear however that the weight of thymus in the castrated animals is markedly greater than in heifers (which are of course unspayed) and bulls. DO 0 d0 U: > 4 o bs _ aa PI, P., _4N -4 m A C9 0 w bo ba O 0 C4 C9 IV 4 P.- to u0 Pa. to UD 140 grs. Oxen Oxen 130 grs. 120 grs. 110 grs. Heifers 100 grs. Oxen 'Heifers Bulls 90 gra. 80 grs. 70 grs. Bulls 60 grs. 50 grs. 40 grs. 30 grs. 0 grs. Heifers Bulls Fig. 1. Showing average weight of thymus in grams. Fig. 2. Showing weight of thymus in grams per 100 kilos. of body-weight. The average weight of thyryus in grammes per 100 kilogrammes of body-weight, as indicated in Fig. 2, is seen to be more uniform than the actual weight. In this relation the thymus weight in the oxen is slightly more than double that of the bulls, while there is a considerable similarity of outline in the curves which respectively indicate their comparative atrophy. In this relation the heifers occupy a position between the oxen and the bulls, but still their excess of thymus weight over that of the bulls is much less than is the excess of thymus weight of oxen over theirs. Their curve is quite different from

4 THYMUS AND SEXUAL ORGANS. those of the oxen and bulls, but this may possibly be due to the fact that there existed a greater disparity in condition among the heifers than among the oxen and bulls. While collectiing the above statistics it was observed that in bulls which had been used for serving cows, and in heifers which had been pregnant for several months, the thymus exhibited a much more marked atrophy than was the case with those which had not exercised the reproductive function. This is shown in Table II and Fig. 3. The weights recorded in this table are included among those of Table I, and Fig. 3 is constructed from Table II. The figures within brackets indicate the number of animals investigated. Age months 12-21,, 2-21 years 3--34, TABLE II. Showing weight of thymus in grammes per 100 kilogrammes of body-weighlt. Heifers. -_k_ Bull&. Not in calf In calf Breeding (7) (7) (2) (11) (2) 70*11 (1) Not breeding (4) (5) (8) (3) (6) (2) (2) 33*33 (2) grs. X1 Prostate not developed grs. 90 gre. 80 grs. 70 gre. 60 grs. 50 gr. 40 grs. Prostate large 30 grs. 20 grs. Not breeding Breeding Fig, 3.

5 226 J. HENDERSON. In judging which bulls had been in service, attention was directed to features indicating completer masculinity, e.g. increased volume of crest and superior muscular development, as well as the specific results of service, namely, special muscular development of the hip muscle and full development of the prostate gland. It will be observed that in Chart III the curve of the not breeding bulls indicates a steady progressive atrophy of the thymus, while the curve of bulls used for breeding indicates an irregular, but on an average greater, atrophy of the gland. The thymus weights in grammes per 100 kilos. of body-weight in heifers recorded in Table II furnish rather instifficient data upon which to found definite conclusions, because unfortunately there are only three in the pregnant class. Still the fact that two heifers under two years old showed thymus weights averaging 34@52 is significant of thymus atrophy greatly exceeding that of the non-pregnant heifers of similar age which averaged Effect of castration upon the thymus gland in guinea-pigs and rabbits. Dr Noel Paton informs me of the following experiments made by himself upon guinea-pigs. Exp. 1. Two guinea-pigs were born in the Laboratory. One, A, was eastrated three days after birth. A B At birth their weights were grs. 80 grs. After a month and a half Thymuses of A and B removed Weights of thymuses * 2 Weights of thymuses per 100 grammes body-wt... * Weights of thymuses per kilogrammes body-weight 1.19 *72 When the thymus weight in grammes per kilogramme of body-weight is calculated in order to bring the experiment into correspondence with the observations on cattle it is found that the normal thymus weight is *72 grammes, while that of the castrated guinea-pig is This demonstrates rather the excessive growth of thymus otn the part of the castrated animal than atrophy in the normal one, because in Paton and Goodall's paper, p. 53, in the normal guinea-pig the thymus increases in size up to two months or until the animal attains a weight of over 300 grs., at which period it becomes capable of reproduction, and it is only after this period that atrophy of the thymus begins. In this experiment the thymus was excised wlhen the animal was 45 days old.

6 THYMUS AND SEXUAL ORGANS. 227 Exp. 2. The second experiment was with a guinea-pig castrated when it weighed 95 grs. and aged 48 hours. Three months after it was chloroformed and weighed grs. Weight of thymus Weight of thymus in grammes per kilogramme of body-weight 2 01 No control was kept in this experimnent, but in their paper (loc. cit.), p. 53, the weights of thyinus in grammes per 100 grammes of bodyweighlt are recorded in four guinea-pigs weighing over 400 grammes, the average of which is -03. By using this as a control and converting it into grammes per kilogramme of body-weight we finid that while the thymus weight in the normal guinea-pig is *3 grs. per kilo., that of the castrated guinea-pig is The difference indicates both the excess of thynius growth in the castrated, and the atrophy of the same in the normal gtiinea-pig. So far as these experiments go they indicate that castration causes persistent growth and arrest of atrophy in the thymus glands of guineapigs. But, as it was evident that results might be more rapidly procured from a study of cattle, the investigation was not continued, The only paper on the subject which I have been able to find is by Dr A. Calzolaril. His observations were made upon male rabbits. He castrated six of them at ages varying from one to three rnonths, and killed them at different periods up to nine months anid compared each with a control of a similar age. He concludes that castration delays the atrophy of the thymus gland. SUMMARY. 1. Castration in cattle causes a persistent growth and a retarded atrophy of the thymus gland. 2. Castration has a similar effect in guinea-pigs and rabbits. 3. In bulls and unspayed heifers the uormal atrophy of the thynmus which begins after the period of puberty is greatly accelerated when the bulls have been used for breeding and when the heifers have been pregnant for several months. I Archives Italiennes de Biologie, xxx. 1898, p. 71.

7 228 J. HENDERSON. APPENDIX. Weight of cattle in kilos. and of thymus in grammes'. I. Age: 9-15 months. (Permanent central incisors absent or erupting.) A. Ox. B. Heifers. C. Bulls. Weight in Thymus Weight in Thymus Weight in Thymus kilos. in grms. kilos. in grms. kilos. in grms II. Age: months. (Eruption of permanent central incisors complete.) A. Ox. B. Heifers. C. Bulls. Weight in Thymus Weight in Thymus Weight in Thymus kilos. in grms. kilos. in grins. kilos. in grms III. Age: 2-2k years. (Permanent central and first lateral incisors erupted.) A. Ox. B. Heifers. C. Bulls. Weight in Thymus Weight in Thymus Weight in Thymus Weight in Thymus kilos. in grms. kilos. in grms. kilos. in grms. kilos. in grms The weights were taken to 0-01 kilo. and these figures were used in the construction of the tables in the text. 2 Breeding. 3 With calf.

8 THIYMUS AND SEXUAL ORGANS. 229 IV. Age: years. (Permanent central, first and second lateral incisors erupted.) A. Ox. Weight in kilos. Tihymus in grms. Weiglht in kilos. Thymus in grms B. Heifers. Weight in kilos. Tliymus in grms C. Bulls. Weight in kilos. Thymus in grms With calf. 2 Breeding.