DIGESTIVE ACTIVITY OF MESENCHYME. 105 



As these cells advance toward the injected mass they exhibit 

 a series of changes, which make them rapidly acquire an entirely 

 different structure and unroll a digestive activity little expected 

 from the small lymphocytes. A rapid transformation of a small 

 lymphocyte into a histiotopic wandering cell thereby takes place. 

 Analogous changes have been observed in small lymphocytes, while 

 in grafts of adult splenic tissue, the small lymphocytes wander out 

 from the grafted tissue into the intercellular spaces of the allantois. 

 Both nucleus and cytoplasm of these cells increase in size. The 

 cytoplasm does not become more basophilic, as usually is the case 

 with the hypertrophying mesenchymal cells. It stains light blue 

 with Azur II., and is often pervaded with minute vacuoles. The 

 nucleus grows also ; its chromatin, especially in the early stages, 

 appears as in small lymphocytes in the form of irregular, rather 

 heavy particles, but is soon converted into tiny fragments. The 

 cells now differ entirely from the small lymphocytes in morphologi- 

 cal appearance and wherever found in contact with edestin gran- 

 ules, rapidly ingest them. 



The small lymphocytes are scarce in the circulation of a normal 

 tadpole and the appearance of a great number of these cells, not 

 only around, but in later stages within the injected mass, is at 

 first glance rather difficult to account for. A study of the organs 

 of the tadpole at this stage has revealed that the chief hemopoietic 

 center is situated in the kidney. The blood-forming processes 

 here exhibit a peculiarity not yet described in any hemo- 

 poietic organs of other embryos. The young blood stem cells, 

 in the form of the lymphoid hemoblasts (large cell, basophilic 

 cytoplasm, clear, round nucleus with a well- formed nucleolus) 

 are here extremely scarce. Lymphoid cells are present in great 

 numbers, but they exhibit the structure of small lymphocytes. 

 The reciprocal relations of the blood cells in the kidney of the 

 tadpole cannot be discussed at present, but it may be pointed out 

 that the same characteristic feature was observed by one of us in 

 the case of the axolotl years ago while studying the hemopoiesis 

 in the perihepatic tissue in this animal. 



The vessels in the kidney of the tadpole under experiment are 

 always found to contain numerous small lymphocytes and an 



