LUDWIG AND MODERN PHYSIOLOGY. 17 



came out in 1852, the book which gave the coup de grace to 

 vitalism in the old sense of the word, his method of setting 

 forth the relations of vital phenomena by comparison with 

 their physical or chemical counterparts, and his assertion that 

 it was the task of Physiology to make out their necessary 

 dependence on elementary conditions, although in violent 

 contrast with current doctrine, were in no way surprising to 

 those who were acquainted with the then recent progress 

 of research. Ludwig's teaching was indeed no more than 

 a general application of principles which had already been 

 applied in particular instances. 



The proof of the non-existence of a special " vital force " 

 lies in the demonstration of the adequacy of the known 

 sources of energy in the organism to account for the actual 

 day by day expenditure of heat and work — in other words, 

 on the possibility of setting forth an energy balance sheet in 

 which the quantity of food which enters the body in a given 

 period (hour or day) is balanced by an exactly correspond- 

 ing amount of heat produced or external work done. It is 

 interesting to remember that the work necessary for 

 preparing such a balance sheet (which Mayer had attempted, 

 but, from want of sufficient data, failed in) was begun 

 thirty years ago in the laboratory of the Royal Institution 

 by the Foreign Secretary of the Royal Society. But the 

 determinations made by Dr. Frankland related to one side of 

 the balance sheet, that of income. By his researches in 1 866 

 he gave Physiologists for the first time reliable information 

 as to the heat value {i.e., the amount of heat yielded by the 

 combustion) of different constituents of food. It still re- 

 mained to apply methods of exact measurement to the 

 expenditure side of the account. Helmholtz had estimated 

 this, as regards man, as best he might, but the technical 

 difficulties of measuring the expenditure of heat of the 

 animal body appeared until lately to be almost insuperable. 

 Now that it has been at last successfully accomplished, we 

 have the experimental proof that in the process of life there 

 is no production or disappearance of energy. It may be 

 said that it was unnecessary to prove what no scientifically 



sane man doubted. There are, however, reasons why it is 



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