412 Dr. C. Shearer. Heat Production and Oxidation 



ment was initiated the heat production rose steadily without pause or 

 interruption. It followed the oxygen consumption closely in all respects, and 

 like this, showed no direct relationship to the rate at which morphological 

 organisation took place within the egg. No heat production could be 

 observed during the formation of the fertilisation membrane or the early 

 phases of the fertilisation process itself. 



In all Meyerhof's experiments great over-crowding of the eggs necessarily 

 took place, and it is difficult to believe that under such conditions the heat 

 production was normal. In attempting to repeat his experiments, using a 

 much larger vacuum flask and a smaller quantity of sea-urchin eggs where 

 they were less crowded, I was unable to get them to fertilise in the closed 

 flasks. As Loeb first pointed out, an abundant oxygen supply is the 

 invariable constant required by the fertilised and developing egg-cell. In 

 my own experiments, in order to get. my eggs to fertilise and segment 

 regularly, I was forced to adopt some means of keeping them aerated during 

 the course of the experiment. If large quantities of eggs were employed 

 (300-400 mgrm. of egg nitrogen), then it was absolutely necessary to carry 

 out artificial aeration, or otherwise a large number of the eggs quickly died 

 and soon cytolysed, and during cytolysis liberated an abnormal amount of 

 heat. As I have shown with bacteria (3), the death process and cytolysis of 

 all cells is probably accompanied by an abnormally high oxygen consumption 

 and heat liberation. On these grounds Meyerhof's experiments seemed open 

 to criticism. It was worth while repeating his experiments, using different 

 methods which avoided, as far as possible, this difficulty. Moreover, it 

 was of interest to determine if a different method of measuring the heat 

 liberation would give figures similar or of the same order as those obtained 

 by Meyerhof. 



The Winkler titration method employed by Meyerhof in estimating the 

 oxygen consumption of the egg on fertilisation and development is somewhat 

 unsatisfactory in that it probably gives too high a figure for the oxygen 

 consumption of the egg. The sea-urchin egg on fertilisation discharges a 

 certain amount of organic slimy material into the sea-water, which interferes 

 to a considerable extent with the accuracy of the titrations carried out by 

 this method. The following experiments are for these reasons, to a large 

 extent, a repetition of Meyerhof's work, using different methods for both the 

 heat measurement and the oxygen consumption and carbon dioxide output 

 of the egg. The eggs and sperm of Echinus miliaris were employed. This 

 species being a shore form it is exceptionally favourable for work of this 

 kind. It can be readily reared to the adult stage in small culture jars under 

 laboratory conditions. 1 have shown, working in conjunction with 



