Functions of the Thymus 



47 



walls of this branching tube (fig. 31), and its epithelium becomes broken 



up and modified to form the reticulum and concentric corpuscles of the 



medulla. In Petromyzon the thymus retains its 



original connexion with the branchial clefts, but 



in all other vertebrates this connexion becomes 



lost, and in mammals the organ takes up a position 



either in the neck or in the anterior mediastinum. 



In birds it forms a series of isolated masses 



on each side of the neck. Small portions of 



thymus tissue are frequently found embedded 



in the thyroid, these having developed from the 



sprouts of the fourth branchial pouch ; on the 



other hand, an accessory thyroid is often met 



with in the substance of the thymus. 



The thymus is singularly susceptible to the 

 effects of inanition; even a short period of fasting 

 produces a considerable diminution in its size. 



Functions of the Thymus 



The functions of the thymus are more obscure 

 than those of most of the endocrine organs: 

 indeed there is room for question whether it 

 should be included amongst these bodies. But 

 the mutual relations which appear to be estab- 

 lished between it and the generative glands in 

 the male sex perhaps entitle it to occupy a place amongst them. 



Injection of extracts of the gland seems to have no specific effect. 

 The results of feeding with the thymus appear also to be non-specific ; 

 such as are obtained seem to be dependent upon the large amount of 

 nuclein it contains. But according to Gudernatsch, tadpoles which are 

 fed with thymus do not undergo metamorphosis, although they increase 

 greatly in size : the same observer describes exactly the opposite effect 

 as the result of thyroid feeding. Noel Paton and Goodall, who removed 

 the thymus in a number of guinea-pigs, were not able to establish any 

 relation of the gland to the rate of growth of these animals, which 

 apparently suffered no deleterious effects from loss of the organ. Other 

 observers (Basch, Klose and Vogt, Matti), who for the most part employed 

 kittens and puppies for experiment, have described certain positive results 

 of thymectomy ; especially softening of the bones with increased excretion 

 of calcium salts, muscular weakness often with tremors, and diminution 

 of intelligence. Compensatory increase in amount of the splenic follicles 

 has been described. The symptoms were not alleviated by grafting or 

 by feeding with thymus. 



Klose and Vogt also obtained an increase in rate of development of both 

 the testicles and ovaries. As regards the testicles, this result has been 



Fig. 31. — Section of developing 

 thymus. (From Prenant, 

 Bouin, and Maillard.) 



c, cortex; m., medulla. At this 

 stage the medulla is continuous 

 throughout the gland. 



w/ 



