THE FACTORS WHICH MODIFY THE METABOLISM 191 



work and the extent of metabolism, one is disposed to ask 

 what are the facts regarding mental work. When it is 

 said that mental states have no distinct influence, apart 

 from that which is secondary to the changes in tissue 

 activity which may attend them, a feeling akin to disap- 

 pointment is often manifested. Yet a little reflection will 

 convince one that positive effects are scarcely to be ex- 

 pected. The central nervous system, important as it is, 

 constitutes, after all, only 3 or 4 per cent, of the body. 

 Most of its substance is stable and relatively passive in its 

 nature. If its really active cells were to double their 

 average metabolism the addition to the heat production 

 and carbon dioxid elimination of the subject would not 

 be significant in the totals observed. A slight change in 

 the state of the muscles would suffice to offset and dis- 

 guise it. 



An emotional experience is much more than a cerebral 

 phenomenon. In times of excitement the skeletal muscles 

 are played upon by the nervous system and metabolism 

 in consequence may be largely increased. But this is not 

 the direct result of the brain process; it is merely a special 

 case of muscular activity. An emotion, pleasurable or the 

 reverse, is a kind of exercise and often one of marked inten- 

 sity. This is recognizable in the increased heart action, 

 in the quickened breathing, and in the contractions which 

 bring about characteristic attitudes and expressions. 



Mental application of a kind which can be more or less 

 successfully separated from these muscular accompani- 

 ments cannot be shown positively to affect the metabolism. 

 A short time ago a trial was made at Middletown, Con- 

 necticut, in which a group of students in Wesleyan Uni- 

 versity took bona-fide examinations in a respiration cham- 

 ber which was at the same time a calorimeter. Each man 

 took his turn, spending three hours over his paper and 

 experiencing the usual anxiety and strain attendant on such 

 a proceeding. On other days each subject spent a like 

 period in the chamber engaged in copying printed matter. 

 Thus it was possible to compare in about twenty cases the 



