SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 755 



speculation will remain unprofitable. At the same time, it is quite 

 legitimate to adopt an interim belief, either with Rubner; Richet; 

 and Terroine, that they are the same, or with Pfaundler; Benedict; 

 and LeBreton, that they are different. Certainly all the evidence from 

 chemical embryology supports the latter view. 



4-19. Respiratory Intensity of Embryonic Cells in vitro 



Obviously the only way to decide whether surface is the governing 

 factor in heat-production is to remove the surface, and to see whether 

 the heat-production is then the same. This can be done by experi- 

 ments on respiration in vitro. If in vitro protoplasms respire to a very 

 similar intensity, irrespective of the size and surface of the animal 

 from which they are derived, Terroine will be right, but if not, then 

 LeBreton's thesis will be justified. Unfortunately, results are not 

 unanimous. In 1924 an in vitro diflference between large and small 

 animals was discovered by Meyerhof & Himwich, and denied by Grafe. 

 In the following year, the former workers were supported by Wels, 

 who found that, without exception, the bigger and older the animal 

 the slower was the in vitro respiration. "Eine bestimmte, vom Nerven- 

 system unabhangige Energiewechselgrosse des Gewebes zu den funda- 

 mentalen Arteigenschaften gehort", said Wels. He found, however, 

 that birds had a higher metabolic rate than mammals of equal 

 weight. Fig. 168 constructed from his figures shows the relationships 

 he found. Very similar work was done by LeBreton & Kayser, who 

 got the following figures: 



Roche & Siegler-Soru, thinking that blood would take up oxygen in a 

 more normal manner in the Barcroft apparatus than pieces of tissue, 

 obtained the following figures for the autorespiration of blood : 



Oxygen taken up per Calories produced per 



