426 



THE AMEBIC AN NATURALIST [Vol. LI 



tions for an eni;liroblast can be found in the organism 

 outside the vessels, where hemoblasts develop into 

 granuloblasts or small lymphocytes. If transplanted out- 

 side the vessels, the erythroblasts still developed further 

 into analogous cells, this would mean that the changes 

 which inside the vessels have transformed a polyvalent 

 hemoblast into an erythroblast are irreversible (at least 

 in the organism), tliat they have narrowed the potencies 

 of the erytlirobkist in comparison with its mother cell and 

 have rendered it s])ecific, i. e. univalent and irreversible in 

 its metabolism. Positive results from such experiment, 

 could they be attained, would be of great value; they 

 would prove that definite factors encountered in the nor- 

 mal organism outside of a cell call forth such changes as 

 would be transmitted by the cell to its daughter cells even 

 if the differential factors had no longer direct influence 

 upon them. 



The arrangement of such experiments offers however 

 insuperable difficulties. Hemoblasts or mesenchynud 

 cells can be trans]>hinted, for there are stages in the 

 hematopoiesis of the yolk-sac, iti which capilhn-ies are 

 distended exclusively by liciiiohla.-ts mikI at lliis time 

 they can be transferred into the spjicc- lictwt'cn the 

 mesenchymal cells. Jt would he hnidls i)(»>-il)h' (o pick 

 out from within the vessels crx thi'nl)l;i-i>. in which hemo- 

 globin had already Ijegun to dcxciop. Imr wiiich -till were 

 capable of proliferation. Most foil luuitcl} liic rc(|nired 

 ex]>eriment has heen carried out in a sim Ics of allnntois 

 by nature herself. 



The grafting on the allantois which [ used in my recent 



