414 VERA DANCHAKOFF 



amongst the derivatives of these cells of differentiation products 

 exclusively characteristic of a given germlayer, would be adequate 

 proof of the derivation of the cells in question from that germ- 

 layer. If by means of experimental intervention the cells of 

 the subvascular epithelial layer were transformed into hemo- 

 blasts, their mesodermal origin would be definitely proved. If, 

 on the contrary, a cornification of this layer could be obtained, 

 this would offer strong evidence for their ectodermal nature. 



The allantois w^as used in my recent studies^ on the potencies 

 of the reticular splenic cells as a favorable medium for growth 

 of tissues and development and differentiation of their cells. 

 The various tissues of the allantois, under the condition of the 

 experiments, manifested definite changes; most of them were of 

 progressive nature. Those relating to the subvascular epithelial 

 layer only are of value in connection with the identification of its 

 constituent cells. 



The changes in the cells of the subvascular layer were re- 

 vealed in response to the irritation produced by the apposition of 

 different tissues on the surface of the allantois. Though in 

 nature similar, they differed somewhat according to the stage at 

 which the cells were activated in the course of the experiment. 



A proliferation was brought about not only in cells which 

 were in immediate contact with the graft but also in regions at a 

 distance of 2 to 5 cm. from the graft. A proliferation took place 

 not only at stages in which the epithelial-like layer covered the 

 allantois as a membrane but also at stages in which it occupied 

 a deeper position beneath the vascular respiratory net. In both 

 cases the ultimate changes undergone by the epithelial layer of 

 cubic cells Consisted in cornification of the more mature cells. 



In stages, in which the cubic cells formed a membrane on the 

 surface of the allantois, their proliferation led to a thickening 

 of the membrane. As seen in figure 3 the epithelial membrane 

 of the allantois is now composed of numerous layers of epithelial 

 cells, amongst which in many places three or four different 

 kinds of cells can be recognized. The whole structure of the 



^ Potentialities of the lymphoid hemoblasts of the adult spleen. Proc. of the 

 Am. Assoc, of Anat., 1917, p. 345. 



