KQII VALENCE OF HEMATOPOIETIC ANLACiES. I. SPLEEN 295 



slow ill tlieir response, cannot be definitely determined on the 

 basis of the available experimental material. A similar intense 

 development of lymphoid hemocytoblasts at the expense of 

 reticulmn cells is observed in the pulpa. Thus the stimulation 

 applied at a stage with develo])ed spleen vascularization incites 

 equal reactions through the whole organ. Both in the pulpa and 

 in the follicles this reaction is manifested by an intense sphtting 

 off of lymphoid hemocytoblasts and their intense proliferation. 



A study of further development of such spleens shows, how- 

 ever, that the differentiation of the lymphoid hemocytoblasts 

 develops differently according to their localization in the pulpa 

 or in the foUicle. The study of the normal histogenesis has 

 demonstrated that lymphoid hemocytoblasts, situated in the 

 cavernous tissue of the pulpa, differentiate finally into granular 

 leucocytes; in the reticular tissue of the follicle they develop 

 into small lymphocytes. The same strong dependence of 

 differentiation of lymphoid hemocytoblasts upon the environ- 

 mental structural conditions is observed in a spleen after 

 stimulation. The stimulation stirs up the less differentiated 

 cells, which are the mesenchymal cells and the lymphoid hemo- 

 cytoblasts. The further differentiation is effected in compliance 

 with the conditions met and granular leucocytes are differenti- 

 ated in the pulpa, and small lymphocytes in the follicles.^ 



*It is difficult to harmonize with the results of my present paper, the data 

 given by Dr. Murphy in his recent note regarding the effect of adult spleen 

 grafts on the organism of the hostembryo (Journ. of Exp. Med. July, 1916) in 

 which he states that, "while the spleen of a normal embryo of this age (18 days) 

 presents only a beginning differentiation of cells, after grafting this process is 

 well advanced and numerous cells of both the granular and non-granular type 

 are found." 



.\s seen in figures 7, 8, 9, 10, 12 and 13 of the present paper taken at the 

 11th, 13th and 15th days of incubation a normal spleen presents a highly ad- 

 vanced differentiation of granular cells from the 11th day and a good start of 

 development of small lymphocytes from nearly the 15th day of incubation. 



The changes in the host spleen after grafts at the 17th and 18th day of incu- 

 l)ation, 10-11 days after grafting (the only stages to which Dr. Murphy refers 

 in the above quoted note) present the ultimate results of intense modifications, 

 which are very different from the advanced stage of differentiation mentioned 

 by Dr. Murphy. 



A remarkable stimulation of granulopoiesis can be seen however in early 

 stages.— at the 2nd, 3rd, and 4th day after grafting. A stimulation of develop- 

 ment of small lyin])hocvtes has not been observed as yet. 



