406 BIOLOGY: GENERAL AND MEDICAL 



nator igneus. After ten days, however, pathological 

 conditions were observed and the animal was killed for 

 further and minute study. 



Another combination consisted of an anterior part 

 of Rana esculenta and a posterior part of Rana arvalis 

 and lived for seventeen days. Each half in both of 

 these experiments retained its specific characters, though 

 the circulation was common. 



Harrison had still better results for, having com- 

 pounded an organism of portions from Rana viresceus 

 and Rana palustris, he was able to keep it alive until it 

 changed into a frog, each half of which continued to 

 show its own specific characters. 



The results of transplantations effected in the higher 

 animals are usually what might be predicted. The im- 

 planted part, if superficial, sloughs off; if deep, is absorbed 

 Bert transplanted the tail of a white rat to the body 

 of Mus decumanus where it remained alive; he failed 

 when he tried to graft the tail of a field mouse upon 

 a rat, and he had no success in his attempts to graft 

 the tail of a rat upon the body of a dog or a cat. 



As has been shown, when the skin of a negro is grafted 

 upon a Caucasian, the pigment in the skin disappears, 

 and eventually all trace of the graft is lost if it is not 

 exfoliated en masse. 



The transplantation of sheeps' thyroids into human 

 beings in cases in which the thyroid is functionless has 

 been performed with temporary relief, but absorption 

 of the implanted tissue usually takes place even though 

 the "physiological necessity" that is favorable to suc- 

 cessful grafting seems to be present. 



For many years pathologists have been industriously 

 experimenting in the hope of arriving at some definite 

 knowledge of the nature and cause of tumors. Being 

 unable to apply the cultivation methods with success, 

 and still expecting to find an infectious agent by which 

 to account for these formations, they made many series 

 of experiments by implanting fragments of tumors 



