264 VERA DANCHAKOFF 



not experimentally controlled, upon the localization of the stem 

 cell in the pulpa or in the follicle, in the case of the spleen. The 

 possibility of identical reaction of the stem cells to definite stimuli 

 is, however, not completely excluded. There may be certain 

 kinds of stimuli, which may cause deviation from the normal 

 differentiation of stem cells. A similarity of the reaction of stem 

 cells in different organs may be expected also in case the differ- 

 ent environmental conditions are made alike, or in case the 

 environment is not fully differentiated, as for example in an 

 embryo. 



Under the influence of these premises an observation made by 

 Dr. Murphy of the Rockefeller Institute attracted my attention. 

 He observed 2-3 years ago an enlargement of the spleen in the 

 host embryo after grafts of various tissues. ^ A closer study of 

 this process led me to conclude, that the considerable enlarge- 

 ment of the embryonic spleen is induced by an intense prolif- 

 eration of the young stem cells. This fact seemed to enable a 



1 This observation was not published by Dr. Murphy at the time. While this 

 paper was in press a brief note by Dr. Murphy regarding the general effect of 

 . the spleen grafts on the organism of the host embryo appeared in the Journ. Exp. 

 Med., July, 1916. It appeared after a number of. my papers and communica- 

 tions (Meeting at New Haven, Staff Meeting at the Rockefeller Institute) and 

 after numerous demonstrations to Dr. Murphy of my preparations. Dr. Murphy 

 states in the above quoted note, that at his suggestion I undertook "the working 

 out of the finer histological details of the process," discovered by him. This, 

 in view of the above mentioned facts, I venture to consider unwarranted. 



Dr. Murphy writes the brief note ''for completeness and record," and gives a 

 reference of his previous work, in which "observations were made on the effects 

 of certain organ grafts on the embryo itself. Murphy, Jas. B., Journ. Exp. 

 Med. 1913, vol. 17, p. 482." This paper however does not contain any obser- 

 vation on this subject. The only passage in this paper, referring to the effect 

 of the graft upon the embryo, reads: "Apart from the thin continuation of 

 the chick membrane, which covers the tumor and the ingrowth of vessels with 

 their scant accompanying stroma, there is no histological evidence of reaction on 

 the part of the embryo to the invasion of foreign tissue." Nor is it possible to 

 find the slightest indication about the effect of the grafts in the body 'tissues 

 of the host in any of Dr. Murphy's previous papers. Through personal com- 

 munication from Dr. Murphy I knew about the enlargement of the embryo 

 spleen. By deduction from my previous hematopoietic work I reached the con- 

 clusion regarding the necessary coexistence of analogous changes in other hema- 

 topoietic organs, a conclusion which the results of the experiments undertaken 

 proved to be correct. 



