4IO THE HISTORY OF BIOLOGY 



has been adopted ever since. Helmholtz, who was physicist, mathematician, 

 and biologist, had, in fact, special qualifications for laying down on an em- 

 pirical basis an exact formula for this generally accepted principle, and dur- 

 ing the succeeding epoch it was his name that was most often associated 

 with this radical change in the general conception of nature. It was this very 

 contribution, however, that caused Helmholtz a good deal of unpleasant- 

 ness. In his paper he had made no mention of Mayer, because he was not 

 aware of his first essay, but in a later lecture he fully acknowledged Mayer's 

 priority. This, however, was not enough to satisfy Mayer's admirers; one of 

 them, E. Diihring, a lecturer in philosophy, made an extremely bitter and per- 

 sonal attack on Helmholtz, as if he had sought to appropriate an honour to 

 which he had no right. Disciplinary action was taken against Diihring, but 

 Helmholtz kept silent until Mayer, broken in health, had passed away; then 

 he took up the challenge and pointed out how Mayer, with all due acknowl- 

 edgment both to his genius and to his right of priority, had nevertheless 

 based his views on speculation rather than on empirical research. On this 

 point Helmholtz was undoubtedly right; Mayer was no experimental scien- 

 tist — he never had a laboratory at his disposal — but he was a brilliant 

 thinker who, with the aid of the observations of others and his own ideas, 

 achieved his epoch-making results by theoretical means. The history of 

 natural science proves, however, that theoretical conclusions of this kind are 

 seldom given the same significance as conclusions drawn from the student's 

 own empirical observations — Swedenborg's brilliant scientific speculation, 

 which, though the work of a genius, was nevertheless forgotten by the im- 

 mediately succeeding generations, is of course the classical example of this — 

 and besides through his ill health Mayer was prevented from following up 

 his idea, which he would undoubtedly have done had circumstances per- 

 mitted. As it was, he had to divide the honour with Joule, the experimenter, 

 and Helmholtz, the universally trained thinker and observer; all three con- 

 tributed towards working out the principle of the conservation of energy — 

 certainly the most important theoretical contribution of the past century in 

 the field of natural science. 



Through the principle of the conservation of energy the experimental 

 study of living organisms received a powerful stimulus; immediate steps were 

 taken to apply to as many life-phenomena as possible this new conception, 

 which placed all phenomena in existence, both animate and inanimate, in 

 one single simple and clear causal connexion, and which offered the hope of 

 being able to bring all manifestations of life, even the most complex, under 

 the same simple explanatory principles that physics and chemistry had al- 

 ready adopted. The following decades were therefore a period of brilliant 

 achievement in the field of experimental physiology; both its aims and its 

 methods took definite form during that period, so that in the medical fac- 



