200 HERMANN VON HELMHOLTZ 



and its connexion with metabolism) is principally due to the 

 fact that the heat to be measured is not evolved suddenly, but 

 in the course of hours, so that it cannot be even approximately 

 collected in an apparatus, while further a considerable quantity 

 of air has to be led through such an apparatus, which carries 

 off a good portion of the heat produced, apart from the aug- 

 mentation of work consequent on the necessary size of the 

 apparatus. Within limits, however, experiment shows that 

 the heat actually produced in animal bodies corresponds with 

 that given off in chemical processes. He makes it intelligible 

 that the animal body does not differ from a steam-engine in the 

 way in which it obtains warmth and energy, but only in the 

 objects, and the way and means, for which and by which 

 it uses the acquired energy. In conclusion he points out 

 how the hypothesis of a vital energy has been gradually 

 eliminated by all these experiments, so that the younger 

 scientific workers, who are seeking the true causes for all 

 these processes, no longer admit any distinction in chemical 

 and mechanical work within and without the living body. 

 The law of the conservation of energy points the way in 

 which these fundamental questions, which have given rise to 

 so many speculations, can be really and adequately solved 

 by experiment. 



On May 16, 1861, Helmholtz was married to Fraulein Anna 

 von Mohl. ' Even Helmholtz's closest friends/ writes the sister 

 of his first wife, ' found it difficult to reconcile themselves to his 

 marrying again after only one year. After the ideal happiness 

 of the former marriage such a step, taken so quickly, appeared 

 almost inconceivable. They did him injustice. He did not 

 really lose his wife at the time of her bodily death . . . she 

 had gone from him before, owing to the terrible nature of her 

 illness. For more than a year, her inner life had been dying out 

 step by step, paralysing all her interests and sympathies. 

 Only in death did she regain her old intellectual and moral 

 eminence. Thus Helmholtz had long been a solitary man 

 when she died, and the outlook for the future with two 

 small children and their grandmother, who in spite of all 

 devotion and self-sacrifice was an old woman, was a sad one. 

 For Helmholtz, who was accustomed to the most active mental 

 companionship, it was absolutely impossible. He chose a wife 



