34 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



instance a large series of experiments in order to arrive at correct interpreta- 

 tions and to draw justified conclusions. Such experiments require, therefore, 

 much patience and experience on the part of the investigator, but the problems 

 are of sufficient importance to warrant these efforts. However, after all these 

 conditions have approximately been satisfied, there remain still a number of 

 variable factors in these experiments which have not yet been eliminated ; 

 therefore a complete solution of the problems involved is impossible at the 

 present time and must be left to future work. 



Since multiple transplants of various kinds from the same donor into a host 

 behave in a corresponding manner, a grading of results can be made which 

 express the degree of compatibility between the individuality differentials of 

 donor and host, and thus a standard can be established with which to compare 

 the results obtained in different experiments. The grades chosen for this pur- 

 pose are arbitrary; they range between 1 and 3+ (3.25). In autotransplanta- 

 tion, the grades given are 3+ and 3. The tissues are well preserved and while 

 at first there may be some irregularities in the structure of the grafts, they 

 gradually assume more and more the characteristics of the normal organs, 

 provided some accidental factors do not prevent such a development. Marked 

 lymphocytic infiltration is lacking, but at early periods after transplantation 

 some very small collections of lymphocytes may be seen ; after some time, 

 these cells usually disappear. Likewise, the connective tissue ingrowth into 

 the autotransplant is restricted and an invasion of the fat tissue by small 

 vacuolated cells and by fibrous tissue is lacking. Grades 3— (2.75) and 2 + 

 (2.25) are given if the grafted tissues are, on the whole, well preserved, but 

 if a reaction of the host is definitely noticeable, consisting in various degrees 

 of lymphocytic infiltration and in a somewhat increased activity of the con- 

 nective tissue, which may cause a rather mild injury to the transplant ; reac- 

 tions of this kind may be seen if donor and host are related to each other. If 

 the reactions are somewhat more marked and tend to lead to a partial destruc- 

 tion of the transplant, grade 2 is given ; this indicates a somewhat greater 

 strangeness of the individuality differentials. In typical, more severe homoio- 

 reactions the grades range between 2— and 1. Grade 1 is applied in experi- 

 ments in rats and guinea pigs, in which the thyroid has been entirely destroyed 

 and the fat tissue largely replaced by fibrous tissue; grade 1+ signifies the 

 survival of only a small part of the thyroid gland ; the reaction in the fat tissue 

 is still very severe. Grade 2— (1.75) is given if the thyroid gland is strongly 

 invaded by fibrous tissue and a considerable part of it has been destroyed, but 

 if at least one-half of the organ has escaped destruction at the time of ex- 

 amination. There is usually, in these cases, a definite lymphocytic infiltration, 

 provided the injury to the tissues has not led to a marked diminution in the 

 amount of the individuality differential substance present in or produced by 

 the transplant. If in addition to thyroid, cartilage and fat tissue have been 

 transplanted, corresponding grades may be given in accordance with the degree 

 of survival of the tissues and the degree of lymphocytic infiltration. The addi- 

 tion of ovarian transplants may make possible a still finer grading : in the most 

 favorable cases large follicles and even corpora lutea are found in such grafts ; 



