2 6o TEE POPULAR SCIENCE MONTHLY. 



was the beginning of the series of researches by the aid of which 

 Du Bois-Reymond, Helmholtz, and others have built up the 

 general physiology of the nerves and muscles. It was the first 

 instance, says Du Bois-Reymond, of the examination of an emi- 

 nently vital force as if it were a physical one, and of the mathe- 

 matical expression in figures of the laws of its action. 



Schwann assisted, with the professors at Berlin, in the prepa- 

 ration of the Encyclopedic Dictionary of the Medical Sciences, to 

 which he contributed the articles on vessels, hematose, urinary 

 secretion, and cutaneous secretion. At this period, also, he began 

 the experiments which led up to the discovery of the digestive 

 ferment, pepsin; and the principles which he set forth on the 

 subject are essentially the same as are still taught, the elucidation 

 of a few details being all that has been added. 



In one of the theses attached to his inaugural dissertation, 

 Schwann had opposed the theory of spontaneous generation, 

 which had begun to prevail again, after a general abandonment of 

 Spa'ilanzani's germ theory. The absence of microbes from prepa- 

 rations which had been hermetically sealed was attributed to the 

 deprivation of oxygen. Schwann and Franz Schulze labored 

 independently to disprove this view. Schulze showed that vege- 

 table and animal infusions could be preserved for months in the 

 presence of air and after renewing supplies of air, if the air was 

 first passed over sulphuric acid to kill the germs in it. Schwann 

 communicated to the Society of German Naturalists and Physi- 

 cians the results of similar experiments, and of others in which 

 he destroyed the germs by calcination. He explained putrefac- 

 tion as a work of decomposition by the germs developing them- 

 selves at the expense of the organic substance, in proof of which 

 he showed that arsenic and corrosive sublimate, which were poi- 

 sonous to infusoria, were also the best preservatives against putre- 

 faction. It remained to be shown that the calcination of the air 

 did not deprive it of its essential properties of sustaining respira- 

 tion and promoting alcoholic fermentation — for the advocates of 

 spontaneous generation might say that the development of life 

 was prevented by asphyxiation. Schwann's view was sustained 

 when he found that frogs suffered no inconvenience in calcined 

 air ; but, when it came to apply the test to the fermentation of 

 alcohol, no fermentation took place. Schwann was not discour- 

 aged by this, but proclaiming a new discovery, that yeast was an 

 organic growth, and working out experiments to prove it, con- 

 verted the apparently hostile result into an additional support to 

 his theory. These ideas did not receive at once the support they 

 deserved. They had a formidable adversary in Liebig, who set 

 forth another theory of fermentation, and ridiculed them with a 

 parody. Schwann, averse to controversy, made no answer to 



