192 JOHN STEPHENS LATTA 



under any conditions of environment, will give rise to one type 

 of cell only. 



The monophyletic theory, first advanced by Saxer ('96) and 

 Brj^ce, is, in some form, accepted by most of the more recent 

 hematological workers. 



Among those who most vigorously defend this monophyletic 

 theory are Maximow, who made careful study of hematopoiesis 

 as occurring in various places in the mammalian embryo, and 

 Danchakoff who made investigations similar to those of Maximow 

 in chick embryos, and also, more recently, studied experimentally 

 produced erythro- and granulopoiesis in the spleen of the chick, 

 Weidenreich, Pappenheim, in part, and many others also uphold 

 this view. 



With the histogenesis of erythroblastic tissue so clearly es- 

 tablished by Saxer, Weidenreich, Pappenheim, and especially by 

 Maximow and Danchakoff, it is unnecessary to discuss this in 

 detail. A study of the regions in the connective tissue about the 

 intestinal tonsils, where erythropoietic foci are forming, clearly 

 indicates that the stem cells from which the cells of an erythro- 

 blastic nature develop, are identical, morphologically, with the 

 lymphoid hemoblasts, or so-called germinal center cells of the 

 lymphatic nodules, and, therefore, morphologically identical 

 with the stem cell producing connective-tissue eosinophils; i.e., 

 a cell with a large, rounded or oval clear vesicular nucleus, with 

 scanty chromatin, and one or more prominent nucleoli, and a 

 variable amount of basophilic cytoplasm. 



Subsequent changes of this type of cell to form an adult 

 erythrocyte involve both the nucleus and cytoplasm. These 

 changes of nucleus and cytoplasm are possibly not interrelated 

 in any way, but they do occur simultaneously, and are brought 

 about by conditions affecting the cell as a whole. Cytoplasmic 

 changes are the gradual change from a basophilic to a brilliant 

 acidophilic character, due to the laying down of hemoglobin in 

 it. Nuclear changes are a gradual shrinkage in size, assumption 

 of a pycnotic condition, and finally its extrusion from the cell. 

 Many of the non-nucleated adult erythrocytes (erythroplastids) 

 are found free in the connective-tissue spaces as well as develop- 

 mental stages. 



