Il8 INTERNAL SECRETION 



the thymectomized and the control animals. He found that the 

 amount of strength required to break the bone was much less in 

 the case of the thymectomized than in that of the control animal. 

 Five to seven days after the fracture the callus in the control 

 animal was large, and felt more like a spindle-shaped swelling 

 of the bone ; in the thymectomized animal it was ring-shaped and 

 considerably smaller. The difference in the development of the 

 callus was perceptible for several weeks. The changes in the 

 bones were well shown in skiagrams. In the thymusless animal, 

 the periosteal apposition at the seat of the fracture was slight, the 

 change of the soft parts into bone being only indicated. The 

 difference in the formation of the callus was best seen in 

 suckling puppies, more particularly in cases where the fracture of 

 the bone took place three to four weeks after the extirpation of 

 the thymus. This seems to show that the change in the re- 

 generative processes of the bones does not make itself felt until 

 after a certain time has elapsed. The changed character of the 

 bones is most clearly seen in the hollow long bones, especially in 

 the tibia and femur, and after them in the humerus and the fore- 

 arm bones ; the ribs and the bones of the hand and the foot are, in 

 general, much less affected. 



The examination of anatomical preparations also revealed a 

 distinct backwardness in the development of the bones. In the 

 animals from which the thymus had been removed, the bones 

 were slighter and smaller than in control animals, while the 

 epiphysal lines were frequently broadened and irregular. In 

 two cases there were pronounced changes similar to those seen in 

 the spontaneous rickets of dogs. Microscopic examination showed 

 the changes typical of retarded ossification. In the thymectomized 

 animal, the bone-compact is narrower and contains less lime than 

 in the control animal ; and the bony trabeculas are more fragile 

 and contain a larger proportion of the original cartilaginous 

 formation. There is a larger proportion of cartilaginous tissue 

 at the epiphysal diaphysis line than in the normal animal. The 

 cartilaginous coating of the epiphyses is thicker and more 

 voluminous, and the ossified bony portion is smaller. The long 

 bones of the thymectomized animal take longer to develop ; 

 calcification progresses slowly, and this causes the retardation of 

 growth, the softness of the bones, and the imperfect apposition of 

 the periosteal bony layers after fracture. - 



Basch does not regard the changes which follow extirpation 

 of the thymus as being in any way related to rickets. He is much 

 more inclined to look upon them as disturbances of the develop- 

 ment of the skeleton, more especially affecting the calcification 

 of the bones, and having an etiological connection with the 

 suppression of the thymus gland. The thymus function being 

 only temporary in its nature, it follows that the changes brought 

 about by its suppression are temporary also. Basch believes 



