SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 625 



hypertonic sea water on eggs unfertilised and fertilised. He had found 

 in the previous paper that, although the respiratory rate was practically 

 unaffected when cleavage was stopped by putting the eggs in hyper- 

 tonic sea water, they took up much more oxygen than normally on being 

 returned to ordinary sea water. Thus treatment for varying periods with 

 hypertonic sea water would raise the respiratory rate by a good deal. 

 The rate of unfertihsed normal eggs being taken as i , then the rate of 

 fertilised normal eggs was 6 to 7, that of unfertilised eggs after hyper- 

 tonic sea water 4 to 5 and that of fertilised eggs after hypertonic sea 

 water something like 20. The figures were as follows: 



C.c. oxygen used per hr. 

 Unfertilised eggs : per 28 mgm. nitrogen 



After 75 min. in hypertonic solution 2-3 % sodium chloride 0-29 



„ 105 „ „ 2-3 „ 0-32 



,, 60 ,, ,, 2-3 ,, 0-22 



Fertilised eggs in ordinary sea water 0-30 

 Fertilised eggs: 



After 30 min. in hypertonic solution 4-3 % sodium chloride I 'go 



>» 60 ,, ,, 2-3 ,, 0'7i 



It was noticeable that the utilisation of oxygen by the fertilised eggs in 

 hypertonic solution was not equal to that by the fertilised eggs in sea 

 water plus that by the unfertilised eggs in hypertonic solution, but was 

 much greater. The oxygen consumption seemed to remain at a steady 

 level, and not to rise with time, but it was very little affected by tempera- 

 ture, unlike the respiratory rate of normal eggs in normal sea water. 

 More interesting embryologically was the experiment in which Warburg 

 took eggs at different times after fertilisation, and, placing them in hyper- 

 tonic sea water in order to raise their respiratory rate and get bigger 

 differences, afterwards determined the amount of oxygen consumed 

 by them per hour per 28 mgm. nitrogen. The figures were as follows : 



Time of first cleavage 100 minutes. 



Here was a definite appearance of rising metabolic rate. 



In his third paper Warburg took the eggs of Strongylocentrotus as 

 his material. By using phenylurethane he showed that the processes 

 of cytoplasmic and nuclear division were not very closely bound up 



