334 Food as a Motive Power. [July? 



That Mr. Jukes, forgetting the Geological Society's rules, has felt 

 aggrieved at the refusal to publish in full a paper whose fate he 

 would doubtless have predicted, had he remembered the Society's 

 regulations ;* and (2), that he has precipitately written and printed 

 an attack on the council of the Society without first ascertaining 

 that his recollection of the Society's rules was sufficiently exact — a 

 course which can only be compared to rushing into a law-suit 

 without legal advice, on the strength of vague impressions, and 

 with no real knowledge of facts. t 



III. FOOD AS A MOTIVE POWER 



By C. W. Heaton, Professor of Chemistry to Charing-Cross 

 Hospital Medical School. 



No physiologist now doubts that the force exerted in and by an 

 animal is derived from the combination of the oxygen absorbed in 

 the lungs with the solid or liquid substances formed in the body 

 from the food. Hence it follows that if the body remains un- 

 changed in weight after a certain period of time, the force exerted 

 in it during that period is accurately represented by the calorific 

 value of the food, minus the calorific value of the excreta. If the 

 body has increased in weight, a store of potential energy must have 

 accumulated in it ; whereas if it has diminished, some portion of 

 the force developed must have been derived from the store provided 

 by previous increase. To avoid unnecessary complexity, it is best 

 to assume the first of these cases, that, namely, in which the food is 

 exactly equal to the requirement of the body. 



Whatever intermediate conditions it may assume, there can be no 

 doubt that the force developed in the body is mainly expressed in 

 the final forms of Heat and Mechanical Work. It becomes, there- 

 fore, a problem of the greatest importance both to physiology and 

 to dietetics to determine the relation which these two great factors 

 bear to each other and to the different constituents of human food. 

 Much of the work effected by the muscles is afterwards converted, 

 inside the body, into heat, while some of the heat, that, for instance, 

 which is employed in evaporation, is reconverted into work; but 

 these conversions, although they present the gravest difficulties in 

 quantitative investigations, do not affect the main principles which 

 we have to discuss. 



The first problem obviously is to find from the day's food, the 



* Vol. i., Part 2, 1866. 



t It speaks more for the impartiality of the council of the Geological Society 

 that they refused a plac° to such an eminent geologist for his second paper, 

 than that they granted it for his first against their convictions. — The Editors. 



