SIGNIFICANCE OF GAS EXCHANGE 13 



metry is not to be expected ; it is just in such cases that a comparison 

 would probably be very valuable, and might furnish a clue (a) to the 

 nature of the processes taking place, when these are unknown, or (b) to 

 a quantitative estimation of their extent in cases in which their nature 

 was completely established. All those types of metabolism, common 

 enough among invertebrate animals, which deviate from that accepted 

 as normal for mammals ought, therefore, to be studied both directly 

 by biocalori metry and indirectly by respiration experiments. Several 

 instances in which such an investigation is essential to the understand- 

 ing of the processes taking place will be mentioned in the following. 



An attempt in this direction has so far been made only by Meyer- 

 hof [1911] who studied the eggs of sea urchins and determined the 

 absorption of oxygen as well as the heat production. The Calories 

 produced per gr. oxygen absorbed (or small calories per mg.) are 

 denoted by Meyerhof as the caloric quotient of the oxygen. With 

 the ordinary catabolism of fats, carbohydrates and proteins the caloric 

 quotients vary, as shown above, between 3-5 and 3*15. 



In experiments on aquatic animals in which the oxygen is pre- 

 sented in a dissolved form, while the CO 2 liberated remains in a dis- 

 solved state and enters into combination with the carbonates of the 

 sea water, certain corrections have to be applied to the observed caloric 

 quotients in order to make them comparable to those obtained on air- 

 breathing animals. The corrections amount, according to Meyerhof, 

 in the case of the Echinoderm eggs, to - 0*176 Cal. per gr. O 2 , but in 

 the opinion of the writer the estimation is somewhat arbitrary. 



Meyerhof found on eggs during segmentation caloric quotients of 

 2'6 (average, corrected), which is much below any of the possible quo- 

 tients for normal catabolism. For the spermatozoa of the same animal 

 (Arbada) the quotient was about 3*1 or possibly normal, and for the 

 eggs of Aplysia about 2*9. Meyerhof points out that in all cases a 

 catabolism of fat (quotient 3*3) takes place, but assumes that this must 

 be accompanied by other oxidations of an unknown nature and having 

 a much smaller caloric quotient. 



