Il6 INTERNAL SECRETION 



to these results later, and in 1906 published a detailed account 

 of his investigations. Before discussing his discoveries in detail, 

 however, it will be well briefly to describe the results obtained by 

 means of extirpation by certain other authors. 



Cozzolino removed the thymus from young rabbits weighing 

 300-400 grm. and, in the first two months after operation, was 

 able to .find no, change in their condition. In a second com- 

 munication, however, he describes crookedness of the legs, arrest 

 of growth, swelling of the tendons, and progressive cachexia 

 in an animal upon which he had operated three months previously. 

 The histological changes were : irregular proliferation of the 

 cartilage in the region of the epiphyses, which were swollen, and 

 considerable new formation of vessels in the bones. 



S. Vincent did not observe any change in the condition of 

 guinea-pigs after extirpation of th.e thymus. 



Noel Paton and Goodall found that extirpation of the thymus 

 produced no effect upon the growth and development of new-born 

 guinea-pigs. The number of the red blood-corpuscles was un- 

 changed, but up to the age of 2 months there was a reduction 

 in the number of all kinds of leucocytes. Thymectomized animals 

 showed the same leucocytosis, inflammatory conditions and 

 artificial infections in pregnancy as normal animals; their resist- 

 ance to the diphtheria toxin was normal, but to streptococci and 

 staphylococci it was slightly reduced. 



Noel Paton arrived at some remarkable results concerning 

 the behaviour of the sexual glands after thymectomy. That the 

 removal of the sexual glands of rabbits is followed by hypertrophy 

 of the thymus, was discovered by Calzolari in 1898. J. 

 Henderson next showed that early castration is associated in 

 cattle with a stimulation of the processes of growth and a retarded 

 atrophy of the thymus. The normal atrophy of the thymus, 

 which begins at the age of puberty, may be considerably hastened 

 in cattle by using the young bulls for stud purposes and by 

 'allowing the heifers to become pregnant. Paton found that the 

 atrophy of the thymus was arrested in guinea-pigs after castration. 

 He also made the interesting discovery that if thymectomy is 

 performed on guinea-pigs before they reach the age of puberty, 

 the operation is followed by a rapid development of the testicles. 



U. Soli found that the weight of the thymus in capons was 

 much larger than in cocks ; in the latter it averages 0.6 grm. to 

 each kilogramme of body weight; while in the capon its weight 

 is 1.16 grm. to each kilogramme of body weight. In Soli's 

 cocks, the removal of the thymus produced a reduction in the 

 weight of the testicles. 



It seems probable from these results that the thymus exercises 

 an inhibitory influence upon the development of the testicles, and 

 the appearances seem to show that the involution of the thymus 

 is consequent upon the maturity of the sexual glands. 



