SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 623 



may mention a few more of the older ones which have a special 

 interest. Audouin; Baumgartner; and Prevost & Dumas all con- 

 cluded that about three litres of carbon dioxide were lost during 

 the incubation period by one hen's egg of approximately 50 gm. It 

 is striking that, although Audouin's work, for example, was done in 

 1827, their value should have been so correct, for Bohr & Hasselbalch 

 72 years later obtained a figure of 3-032 litres. It is also interesting 

 that the values which Pott and Nessler obtained for weight loss come 

 very close to those of twentieth-century workers. 



Early work on heat-production was, of course, much rarer. 

 Barensprung in 1 85 1 ascertained by the use of a thermometer that 

 hen's eggs in course of development were one-tenth of a degree 

 hotter than the circumambient air, and Ruffini made a similar 

 observation on toad's eggs. Murray had claimed as early as 1826 

 that the albumen at the blunt end was a degree or two hotter 

 than that at the pointed end. In 1872 Moitessier compared the 

 rate of cooling of fertile and infertile hen's eggs and found that 

 the latter cooled more irregularly, perhaps because of the allantoic 

 circulation. 



4-2. Respiration of Echinoderm Embryos in General 



Among the eggs of aquatic animals those of echinoderms have 

 been much investigated with regard to their respiration and heat 

 production, and they have a good deal to tell us about the 

 gaseous exchange of the embryo. The first paper on the subject 

 was that of Lyon, who stated that he had observed a rhythmically 

 increasing and decreasing production of carbon dioxide during 

 cleavage stages in Arbacia eggs, but as he pubUshed no figures in 

 support of this affirmation his paper did not provoke much interest. 

 The first work of importance was done by Warburg in 1908. Using 

 the eggs of Arbacia pustulosa, he determined the oxygen consumed in 

 a given time and at different temperatures by the Winkler method. 

 Instead of weighing the eggs, he introduced the method of doing 

 Kjeldahl nitrogen estimations on them, and of referring the oxygen 

 consumed per hour to these figures, instead of to weight, on the 

 assumption that the total protein content of the eggs remains constant 

 through all the early stages. This was subsequently justified by Rap- 

 kine, who measured the wet and dry weights of sea-urchin's eggs. 

 Warburg paid careful attention in this work to the possible errors 



