4o8 THE HISTORY OF BIOLOGY 



retaining its normal heat. But then there must also be a definite ratio between 

 the heat produced by combustion in the body and the work that the body 

 performs during a given period, or, in still more general terms, a certain 

 amount of heat must correspond to a certain amount of work. Upon his re- 

 turn home Mayer published in Liebig's Annalen der Chemie in 1841 an essay 

 in which he expounded his theory, and in connexion therewith the method, 

 which is still in use, of calculating the dynamical equivalent of heat when 

 the unit of heat represents the amount it takes to heat up a given quantity 

 of water one degree, and the unit of work represents the force required to 

 lift a given weight to a given height — in our days one kilogram one metre. 

 For this ratio he gave a number, which, however, was later found to be in- 

 correct. Shortly after the publication of Mayer's report the English physi- 

 cist J. P. Joule published a theory based on years of experiment and having 

 the same gist as Mayer's, but giving a more correct number to represent the 

 heat equivalent; moreover, it was founded on more substantial proofs and 

 supported by a greater number of facts. Then in the year 1847 came out 

 Helmholtz's essay Von der Erhaltung der Kraft, in which the law of the in- 

 destructibility of energy was elucidated from all points of view and was given 

 its mathematical formula. During the succeeding years, however, Mayer had 

 further elaborated his theory; of particular value to biology was his essay 

 Die organische Beivegung in ihrem Zusammenhange mit dem Stojfwechsel, which was 

 printed in 1845 as a pamphlet because it was refused by the editors of scien- 

 tific journals. In this essay he applies the law of the indestructibility of en- 

 ergy to the vital phenomena in the animal and vegetable kingdoms, gives 

 an account of the mutual relation between muscular action and the digestion 

 in the body's exertion of energy, and at the same time shows the process of 

 assimilation in plants to be the foundation of life on the earth, and solar 

 energy to be its ultimate source. In consequence of this he feels it to be 

 superfluous to assume a special life-force as a source of the metabolism in 

 the living body. This caused but little feeling of satisfaction amongst the 

 biologists of his age; as a matter of fact, the whole theory of the nature of 

 force met with opposition even on the part of the older physicists. When 

 this theory eventually won the day, Mayer considered that due attention 

 had not been paid to his right of priority. This wounded his naturally sen- 

 sitive feelings, which were exposed to still more serious shocks in the year 

 of the revolution, 1848; he was, in fact, from both a political and a religious 

 point of view, strictly conservative, with the result that he joined a differ- 

 ent camp from that of the majority of natural scientists, who were for the 

 most part liberals, and besides he fell out with his brothers, who took part 

 in the revolution. As a result of all these vicissitudes his nerves were com- 

 pletely shattered; finally, after an attempt at suicide, he had to be placed 

 under restraint, and in accordance with the custom of the time he was put 



