CRITERIA OF SUCCESS OR FAILURE 137 



transplantations in fowl. But in all these experiments, as well as in subsequent 

 ones, the principal problem was the study of the conditions which permit 

 successful transplantation and of those which prevent it. However, a second 

 problem soon became prominent: transplantations of organs with internal 

 secretion were used also in order to determine the effects of certain hormones 

 on the growth and functions of various tissues and organs. As examples of 

 transplantations of the latter kind, the experiments of Steinach on the fem- 

 inization of male guinea pigs and rats, by implantation of ovaries into cas- 

 trated males, and on the masculinization of female guinea pigs by the grafting 

 of testes, and those of C. A. Pfeiffer on the effect of transplantation of testes 

 on the endocrine function of the anterior pituitary gland may be mentioned. 

 Both of these investigators carried out transplantations into litter mates and 

 into very young animals. Steinach used castrated guinea pigs, and Pfeiffer, 

 non-castrated rats, as hosts. In the latter experiments, the proportion of 

 testicles in which the tubules survived was relatively great. In both series of 

 investigations we have therefore to deal with syngenesio- rather than with 

 homoiotransplantations. The analysis of individuality was not the principal 

 objective in the large majority of these experiments. A further consideration 

 of all the numerous experiments in transplantations which have been made 

 during the last fifty or sixty years would therefore not contribute much to a 

 fruitful analysis of individuality, and it is not needed because resumes of 

 these investigations have already been given by various authors. 



However, we shall here attempt, if possible, to find the main factors which 

 caused the differences in the results in transplantations of tissues obtained by 

 various investigators, and in particular the differences in their interpretation 

 of these results. One of the principal differences concerns the question as to 

 whether transplants may survive after homoiotransplantation, and whether 

 they survive as well after homoiotransplantation as after autotransplantation. 

 As already mentioned, especially in earlier investigations the view is fre- 

 quently expressed that various homoiotransplanted tissues or organs survive 

 as well as autotransplanted ones ; but this view occurs also even in the more 

 recent literature. This may be due (1) to the lack of differentiation between 

 real homoiogenous and syngenesious transplantations, the latter succeeding 

 better than the former; (2) to the disregard of the age of the transplants; it 

 seems that organs from newborn donors can be more readily transplanted than 

 organs from older donors, and likewise, that the reactions may be milder after 

 transplantations into very young than into older hosts; (3) often to the lack 

 of a complete microscopical examination of the transplants. The smaller 

 transplants should be cut into serial sections and many sections should be 

 available for study from the larger transplants. It is necessary that all im- 

 portant stages, from the beginning of transplantation until the reaction is 

 definite, be examined in succession, and that the various modes of reactions 

 on the part of the host — cellular as well as bodyfluid reactions — be considered 

 and evaluated in as quantitative a manner as possible; and lastly, it is im- 

 portant, if there is a limit to the periods when examinations can be made, that 

 such stages be selected as would permit the recognition of the presence of 



