SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 633 



same type as the normal respiration, judged by behaviour towards 

 ethyl urethane. He tried the effect of adding acids of various kinds 

 and other substances to the Breis, and the inhibiting effect of the 

 cyanide ion was cleared up on the supposition that iron-catalysed 

 oxidations were the main ones taking place in the eggs. 



About this time Loeb & Wasteneys undertook an examination of 

 the temperature coefficient of embryonic development in the sea- 

 urchin's tgg as related to the temperature coefficient of its respiratory 

 rate. This investigation has already been referred to in the section 

 on growth (p. 525). In another paper they showed that fertilisation 

 in Arbacia eggs led to a three to four times rise in respiratory rate, 

 thus confirming Warburg's work on Strongylocentrotus. 



Warburg did not omit to study the effect of varying oxygen 

 tensions on the respiration of his echinoderm eggs. This question, 

 a part only of a very general perplexity which has confused physio- 

 logists for many years, he answered by the finding that respiration 

 was relatively unaffected by changes in partial pressure of oxygen. 

 In his 1908 paper, he said, "The oxygen-concentration was so ar- 

 ranged that it did not sink to below f of its original value, but I 

 found that even if it sank to J, absorption proceeded quite regularly". 

 Two years later he said, "I have shown that the rate of oxidation 

 in the egg is independent of the oxygen pressure, i.e. the oxygen 

 concentration in the egg, although this oxidation-rate can be 

 markedly influenced by alterations in various external conditions". 

 Warburg's figures were as follows : 



Later, however, Henze went into the matter in a research which 

 included work with anemones, gephyrean worms, and many other 

 marine animals. His conclusion was that Warburg's sea-urchin eggs 

 had not been well enough shaken, for a typical result of his own was 



