Reserve Energy of Embryonic Tissues. 



135 



About the fragments of 4- and 5-day-old chick embryos in an 

 atmosphere of pure nitrogen, the heart muscle cells were seen to 

 grow a short distance out into the medium, and there was also 

 an active growth and division of the serosa cells. A similar growth 

 of cells was also seen about the fragments of the body wall. Divid- 

 ing figures were seen in both types of cultures. 



This growth commenced generally, however, only after a 

 considerable latent period varying from 10 to 24 hours. It 

 continued actively for only a few hours, when it ceased and an 

 active rounding of the cell and fragmentation of the nucleus and 

 the cytoplasm intervened. 



In 7.48 per cent, oxygen or in air, this growth commenced 

 always much earlier even after one or two hours. It continued 

 actively for from 24 to 72 hours, when it slowly ceased. The cells 

 did not disintegrate at once, but very slowly. Even after weeks or 

 months, many have been found in a good state of preservation. 



No growth was seen in the cultures of 10- or 1 5-day-old embryos 

 in an atmosphere of pure nitrogen. A growth comparable to 

 that of the younger embryos in pure nitrogen occurred about the 

 fragments of 10-day chick embryos in an atmosphere containing 

 1.8 per cent, oxygen, and about the fragments of the 15-day-old 

 chick embryos in an atmosphere of 5.4 per cent oxygen in nitrogen. 



The results of these observations are graphically shown in the 

 accompanying table and curve. 



Heart muscle fragments of young chick embryos or the whole 

 hearts will contract at once, when placed in the plasma of a tissue 

 culture and warmed to the temperature peculiar to them. Frag- 

 ments of older chick embryos and fetal chickens will not contract 

 in the culture until a certain amount of growth and movement has 

 taken place. 



Fragments of the heart of 4- and 5-day-old chick embryos 

 were found to contract actively in an atmosphere of pure nitrogen 

 for as long as 5 or 6 hours. After this time the contractions became 

 generally weaker, but often did not cease entirely for from 20 to 

 24 hours. 



Conclusions. 



1. These experiments with the contracting heart muscle 

 fragments are in complete harmony with Fletcher's much earlier 

 ones. 



