518 METHODS OF GAS EXCHANGE STUDIES 



sick bed. This method is only suited for brief experiments 

 (minutes up to several hours), particularly in determining 

 the effect of muscular effort, individual nutrient materials 

 and medicinal agents, etc., but not for estimating the metab- 

 olic exchange over longer periods. Magnus-Levy 4 expresses 

 the following opinion of the Zuntz method : * ' For exact meas- 

 urement of the actual exchange for a whole day or longer 

 the twenty-four experiments are absolutely authoritative. 

 Only from them can we learn to practically realize the nutri- 

 tional requirements, etc. ; they constitute the exact basis for 

 quantitative consideration of scientific and, too, practical 

 questions in nutrition. The method makes it possible to 

 fully collate all the influences bearing upon metabolism. 

 However, it is not so well adapted for the precise determina- 

 tion of the value of each individual external factor. Where 

 it is essential to have as sharp differentiation and determina- 

 tion as possible of such influences experiments of short dura- 

 tion are of more significance, and, because of their readier 

 technic, have come to occupy a very much greater field. 

 This is especially true where one is dealing with the estima- 

 tion of relatively small differences. " 



Other Methods. Among other forms of apparatus de- 

 signed for the measurement of gas interchange may be men- 

 tioned the head respiration apparatus of E. Grafe, 5 which is 

 snugly adjusted by means of an inflatable rubber collar ; also 

 a new transportable respiration apparatus of Benedict; 6 

 and, lastly, a device of Douglas, in which the exhaled air is 

 collected in a bag which the subject carries on his back, and 

 after the close of the experiment analyzed. 



Eecent forms of respiration apparatus satisfying modern 

 requirements and used for small animals have been con- 



* A. Magnus-Levy, 1. c., p. 212. 



E. Grafe (Med. Clin., Heidelberg), Deutsch. Arch. f. klin. Med., 95, 529, 

 1909; cf. also Zeitschr. f. physiol. Chem., 65, 1, 1910. 



8 F. G. Benedict (Carnegie Lab., Boston), Amer. Jour, of Physiol., 24, 345, 

 1909. 



