102 Metabolism of Healthy Max. 



meriting, a number of individuals (6 to 10 or more) were placed in a large 

 respiration chamber and the combined carbon-dioxide excretion of the group 

 of individuals was studied, there being no attempt made to distinguish the 

 differences in the metabolism of individuals. This method gives a true average 

 of the group. Furthermore, a number of different groups were studied, thus 

 giving an idea regarding the constancy of groups of individuals, and it was 

 inferred that if groups similar in physical constitution, muscular activity, etc., 

 gave constant results, individuals would likewise give constant results. 



Sonden and Tigerstedt recognized the importance of securing a value which 

 would be as truly representative as possible for the one factor of metabolism 

 they were measuring, namely, carbon dioxide, and devoted special attention 

 to the determination of this factor with the greatest degree of exactness. By 

 means of a modified Pettersson apparatus, Sonden ' was able to secure results 

 that were far more accurate than any previously obtained. It is certain, 

 therefore, that the results secured with this apparatus do represent with great 

 exactness the carbon-dioxide production of groups of individuals under the 

 conditions stated in the protocols. 



Individual subject method. While the first method has been used almost 

 exclusively by Sonden and Tigerstedt, the second method has been adopted 

 by a large number of investigators, especially when using various forms of 

 mouthpieces or nosepieces for collecting the products of respiration. In a 

 large number of their experiments, only carbon dioxide has been determined, 

 but in those made by Speck, and Zuntz and his school, and more recently 

 by Chauveau and Tissot, oxygen has likewise been determined. To the second 

 class, also, belong the series of experiments with the respiration calorimeter 

 which has been made in the laboratory of Wesleyan University. In the earlier 

 experiments not only was the carbon dioxide determined but likewise the 

 water-vapor and the heat elimination. More recently, all four factors of the 

 total metabolism the carbon-dioxide output, oxygen intake, water-vapor elim- 

 ination, and heat production have been simultaneously determined, the multi- 

 plication of determined factors thus rendering the whole study more valuable. 

 These experiments were much more time-consuming and laborious than those 

 made with any other apparatus. As but one individual could be studied at a 

 time, it was necessary, of course, to make a large number of experiments and 

 the respiration chamber was in more or less constant use. 



Possible comparison of results by the two methods. It is possible, there- 

 fore, to compare the average results of respiration-calorimeter experiments on 

 a large number of different individuals with those obtained by Sonden and 

 Tigerstedt in their group experiments. Unfortunately, the investigations with 

 the respiration calorimeter could not be extended to cover as large a group of 

 individuals of different ages as did those of the Scandinavian investigators. 



1 Sonden, Zeitschr. f. Instrumentenkunde, 1889, 9, p. 472. 



