ERYTHROBLASTS IN THE PIG EMBRYO 163 



b. The erythrocytes: normal and degenerative changes 



The question arises as to what extent the blood cells taken 

 from these pig embryos were maintained in normal living con- 

 dition in the cultures. In the study in vitro of other tissues such 

 as young connective tissue and nerve cells, the vital condition 

 of the cells may in part be determined by the presence of activi- 

 ties such as growth, extension of cytoplasmic processes, amoeboid 

 movement and cell multiplication. In the case of the erythro- 

 blasts of the 30 mm. pig embryo, however, it is questionable to 

 what extent manifestations of such vital phenomena as just in- 

 dicated can be expected in these cells. For it must be taken into 

 account that the mature nucleated mammalian erythrocyte, as 

 pointed out by Minot, represents a late stage in "the progressive 

 phase of erythrocytic cytomorphosis, the regressive phase of 

 which involves the formation of the non-nucleated plastid, and 

 that consequently as emphasized by Weidenreich ('03) "Wir 

 diirfen nicht vergessen, dass eben die roten Blutkorperchen der 

 Sanger Morphologisch betrachtet degenerierende Zellen sind" 

 (p. 93) . Mitosis and growth in size cannot, therefore, be taken 

 as criteria of life in the mature erythroblasts, for they have already 

 attained their maximum size, nor do they so far as it is at present 

 known, any longer multiply by mitotic division (Minot '12, p. 

 507). The occurrence of small cytoplasmic processes in the eryth- 

 roblasts of the 30 mm. embryo has already been described and 

 the evidence considered for regarding them as normally present 

 in the circulating blood of the embryo. These processes may be 

 found for several days in the cultures, although they gradually 

 become less evident. 



An observation may also be introduced here concerning young 

 erythroblasts in cultures made from the embryonic liver. It is 

 generally recognized that the young erythroblasts in the early 

 stages of their hemoglobin differentiation may still manifest true 

 amoeboid behavior not unlike that observed in leucocytes. In 

 cultures made from the embryonic liver of the pig, these very 

 young erythroblasts could be clearly seen undergoing slow amoe- 

 boid changes in form. This activity could be observed in the 



