146 RESPIRATORY EXCHANGE OF ANIMALS AND MAN 



temperature, 20. They show a wide divergence with regard to re- 

 spiratory activity both when considered per kg. of body weight and 

 when approximately reduced to " surface " units by multiplication with 

 \/W, It is worthy of note that the metabolism of the single warm- 

 blooded animal, the young dog, at low temperature is considerably 

 larger than of the cold-blooded vertebrates. When considered per 

 unit " surface " it is much greater than any other. As the metabolism 

 of this dog did not at 37 differ materially from that of other dogs or 

 of other warm-blooded animals when calculated per unit " surface," the 

 result appears to indicate that the oxidative energy of the tissues is 

 greater in the warm-blooded than in a cold-blooded organism. 



While the metabolism per kilogram is on the whole increasing 

 with decreasing size (Arbacia eggs excepted), the metabolism per 

 unit " surface " decreases with the size though the variations are on 

 the whole not very large. 



In the final table a large number of determinations made at tem- 

 peratures between 15 and 25 (at 20 whenever such were available) 

 have been put together. They show the order of magnitude of the 

 respiratory exchange of the animals in ordinary circumstances. That 

 they cannot claim much confidence is evident enough from the wide 

 differences found by different observers for the same species. 



In reptiles, Amphibia, and fish, values of 0*2 to 0*5 Cal. per 

 kilogram and hour are generally observed on quiet animals irrespective 

 of size, and the figures for Crustacea and cephalopod molluscs are of 

 the same order, but very young animals of all these groups may show 

 much higher values, probably to a great extent on account of their 

 muscular activity. 



In insects the respiratory exchange is always high compared with 

 that of other animals, but as all experiments have been made on a 

 large number of insects at a time, the animals have probably always 

 been very restless, and the figures do not represent anything approach- 

 ing standard conditions. 



In all the lower invertebrates the respiratory exchange is smaller 

 and often much smaller than in the higher, but the proportion of 

 active substances in their bodies is certainly smaller also, and it is 

 possible that the differences per gr. " organ nitrogen " would not be 

 very large. 



In the protozoa the respiratory exchange is very considerable, 

 and the more so the smaller the size. This may be due, however, to 

 the constant activity of these animals. 



