nS RESPIRATORY EXCHANGE OF ANIMALS AND MAN 



earlier stages that it is quite pronounced also when the material is 

 calculated on the basis of body weight instead of surface. As the 

 rate of growth is undoubtedly most rapid at first and declines after- 

 wards, there can be no doubt that growth is not responsible for the 

 high standard metabolism of children above I month. As the very 

 young children certainly on an average possess less adipose tissue than 

 the older ones, the differences cannot, as Benedict and Talbot suggest, 

 be ascribed to differences in the amount of " active protoplasmic 

 tissue". In the opinion of the writer the factor which is most pro- 

 bably responsible for the regular increase in metabolism of young 

 children is the development of the muscular system as such, and per- 

 haps simply the gradual development of a muscular tone. A com- 

 parison of the histological development of the muscles in infants with 

 the variations in their standard metabolism suggests itself, and it would 

 be useful further to have a series of experiments made on one and the 

 same animal (or animals) during the whole period of growth in con- 

 ditions in which muscular movements and if possible also the mus- 

 cular tone could be abolished. 



Variations in Standard Metabolism in the Full-Grown 



Organism. 



The phenomena to be dealt with in the present section are for the 

 most part very obscure in character, not only with regard to possible 

 causes, but also, unfortunately, with regard to the very facts which 

 have in several cases been ascertained only in a vague and general 

 sort of way. The outcome of a discussion of the heterogeneous and 

 scanty material existing is, therefore, less a statement of results than 

 a caution against results, and some suggestions for further research. 



I. Periodic variations. Hanriot and Richet [1891] found diurnal 

 variations in the respiratory exchange of man corresponding to the 

 variations in body temperature, but as standard conditions were not 

 maintained their observations are inconclusive. Johannson [1898] ex- 

 perimenting on himself, and maintaining standard conditions as rigor- 

 ously as possible, found that in the period from 1 2 at night to 8 in 

 the morning the carbon dioxide production was 37 per cent, lower 

 than the average for 24 hours, while in the period from 8 a.m. to 4 p.m. 

 it was 3-5 per cent, higher, and from 4 p.m. to midnight O'l per cent, 

 higher. Johannson himself ascribes the results to unavoidable differ- 

 ences in activity. Magnus-Levy [1894] has obtained similar results 

 on man and also on a dog. Recently Benedict [1915], however, has 



