IMMUNITY AND SUSCEPTIBILITY OF SEA-URCHIN EGGS. 22$ 



last events either alone or together may constitute what is termed 

 liquefaction. 



The results of the experiments given below can, it is believed, 

 be interpreted in agreement with this view of segmentation. 

 They were undertaken primarily as an extension of experi- 

 mental work which had already been done on the action of vari- 

 ous chemical compounds on protoplasmic bodies, but were limited 

 to the study of such action on the eggs of Arbacia at successive 

 periods after fertilization. 



The existence of a rhythm of immunity and susceptibility has 

 been shown already by Lyon in studying the effect of KCN and 

 of lack of oxygen upon the fertilized eggs and embryos of the 

 same form, 1 and it has been found also that many eggs do not 

 segment at all in the absence of oxygen, notably Arbacia 2 and 

 Ctenolabrus? Lyon also found this summer that Arbacia eggs 

 required more oxygen during precleavage and gave off more CO,, 

 during cleavage than at other times. 5 



From these results it may be inferred in analogy to a large 

 number of instances well known in chemistry that at least the 

 ultimate effect of oxygen on the processes conditioning cleavage 

 is the causing of analytic chemical changes ; /. c., fermentation, 

 one might say, occurs and CO 2 is given off, as Lyon found.. 

 Previous to this, however, synthetic processes may take place 

 which in turn as certain preferments become active 4 give rise to. 

 molecular splitting. The result of such analytic change is that 

 increase in osmotic pressure and therefore the creation of that 

 potential difference between it and the surface tension which we 

 have found to be necessary and in the equalization of which both 

 potentials decrease, water is absorbed, and the egg cleaves. 



The hypothesis to be deduced from this and which might serve 

 as a guide in our experimentation is that any method either (i) 

 of preventing this necessary preliminary increase in osmotic 

 pressure, or of compensating it after it has been created, or (2) 

 of increasing it beyond a certain point, will tend to do away with 



1 Lyon, E. P., American Journal of Physiology, VII., i. 



2 Lyon, loc. cit. 



3 Loeb, ]., Archiv fitr die gesammte Physiologie, 1895, LXII. 



4 Cf. Hofmeister, " Chemische Organisation der Zelle." 



5 Personal communication. 



