32 GASEOUS METABOLISM OF INFANTS. 



of an adult. The infant is incapable of giving intelligent assistance 

 in the experiment, neither can its muscular activity be controlled. 

 Furthermore, in adult life, growth has been attained and the energy 

 required is mainly for maintenance and for definite external muscular 

 work, while infancy is a period of rapid growth, at least if normal metab- 

 olism is progressing; the infant, therefore, requires energy both for 

 growth and for maintenance. While the amount of effective mechan- 

 ical work is nil, nevertheless it has been clearly demonstrated that, 

 during the periods of muscular activity incidental to the active life of 

 the infant, there may be a large increase in the total metabolism. This 

 simultaneous requirement for growth and for maintenance makes the 

 study of infant metabolism a doubly complicated problem. 



On the other hand, in studying the metabolism of an adult, one of 

 the greatest difficulties we have to contend with is the complex life of 

 the normal individual — the irregular or intermittent ingestion of food 

 and the various degrees of muscular activity contributing to the sum 

 total of the metabolic changes of the day. It is possible, by means of 

 large respiration chambers, to approximate the normal life of a man of 

 sedentary occupation or even with some degree of muscular activity, but 

 it is practically impossible to duplicate the life of an ordinary individual 

 with its different environments and activities. Consequently with 

 adults it is necessary to secure periods for observation when the subject 

 is without food in the stomach and when there is a minimum amount of 

 activity. With an infant who spends the greater part of his day in the 

 crib, the life complexes can be much more easily studied. The daily 

 life is divided first into eating, sleeping, and crying; later, as the special 

 senses and the intellect develop, to these divisions are added playing 

 and exercise. Throughout the infantile period, therefore, the daily 

 routine is monotonous and regular, with hours of sleep and waking 

 time relatively constant. The diet of the infant is also unchanging in 

 character, consisting for the most part of milk. 



In summing up, we may say that the normal infant is more nearly 

 constant as to its body activity, daily routine, and diet than the normal 

 adult with his higher life complexes. The inability of the infant to 

 assist materially in metabolism experiments, the difficulty of carrying 

 out definite well-known tests with mathematical accuracy, and the 

 impossibility of regulating the muscular activity must therefore be 

 offset by this constancy in diet and daily routine. Hence it is by no 

 means impossible to reproduce the daily routine of infants inside of a 

 specially constructed chamber. 



RESPIRATION APPARATUS. 



In the Nutrition Laboratory and previously in the chemical labora- 

 tory of Wesleyan University, Middletown, Connecticut, various types 

 of apparatus for studying the respiratory exchange have long been in 

 the process of development. Since practically all of the earlier work 



