SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 627 



bically just as rapidly by the unfertilised eggs as by the fertilised ones, 

 therefore the dehydrase systems are equally active in both. "Not the 

 Atmungsferment, but the relation between Atmungsferment and its 

 substrates, is what is changed on fertilisation" (Runnstrom). For a 

 further discussion of these facts and their significance see p. 867 

 and the reviews of Keilin and of Dixon. 



Runnstrom also studied the effect of urethane. Here the inhibition 

 of the respiration of the fertihsed eggs was accompanied by a stimula- 

 tion of the respiration of the unfertiHsed ones, so that the two came 

 to about the same level. Runnstrom found spontaneously occurring 

 instances of inhibited cleavage in which the respiration was normal. 

 He noted that the protoplasm of urethane eggs was much more 

 heterogeneous colloidally than that of ordinary ones. 



An influence which was found to be much more certain in its 

 action and easier to control than hypertonic sea water was found to 

 be the hydrogen ion concentration of the sea water. Herbst and 

 Loeb had found simultaneously that this factor exercised an important 

 influence on the normal development of the echinoderm egg, and 

 Warburg now studied its influence on the embryonic respiration. 

 The results were as follows : 



The more alkaline the sea water the larger the respiratory rate, 

 but not necessarily accompanied by normal development. The in- 

 fluence of the hydrogen ion on the metaboUc rate in the echinoderm 

 embryo was evidently, therefore, not exerted indirectly through the 

 effect on morphological development. After the experiments, the eggs 

 were put back in normal sea water, but the number which reached 

 the larval stage was not great either in the case of the acid ones or 

 the alkaline ones. The effect ofpH on the respiratory rate of Arbacia 

 eggs was afterwards fully studied by Loeb & Wasteneys, and by 

 McClendon & MitcheH. 



The question of how the hydrogen ion concentration brought 

 about this effect was also discussed by Warburg. He showed, by 

 staining eggs vitally with neutral red after the manner originally 

 introduced by Loeb, that the internal pR was not affected by a stay 

 in sea water of abnormal pYl. Later experiments by my wife and 



