566 FRA OMENTS OF SCIENCE. 



have seen, traced the maggots of putrefying flesh to the 

 eggs of flies. But he did not and he could not know the 

 meaning of putrefaction itself. He had not the instru- 

 mental means to inform him that it also is a phenomenon 

 attendant on the development of life. This was first 

 proved in the paper now alluded to. Schwann placed 

 flesh in a flask filled to one-third of its capacity with water, 

 sterilized the flask by boiling, and then supplied it for 

 months with calcined air. Throughout this time there 

 appeared no mold, no infusoria, no putrefaction; the 

 flesh remained unaltered, while the liquid continued as 

 clear as it was immediately after boiling. Schwann then 

 varied his experimental argument, with no alteration in 

 the result. His final conclusion was, that putrefaction is 

 due to decompositions of organic matter attendant on the 

 multiplication therein of minute organisms. These organ- 

 isms were derived not from the air, but from something 

 contained in the air, which was destroyed by a sufficiently 

 high temperature. There never was a more determined 

 opponent of the doctrine of spontaneous generation than 

 Schwann, though a strange attempt was made a year and 

 a half ago to enlist him and others equally opposed to it on 

 the side of the doctrine. 



The physical character of the agent which produces 

 putrefaction was further revealed by Helmholtz in 1843. 

 By means of a membrane he separated a sterilized putres- 

 cible liquid from a putrefying one. The sterilized infusion 

 remained perfectly intact. Hence it was not the liquid of 

 the putrefying mass for that could freely diffuse through 

 the membrane but something contained in the liquid, 

 and which was stopped by the membrane, that caused 

 the putrefaction. In 1854 Schroeder and Von Dusch 

 struck into this inquiry, which was subsequently followed 

 up by Schroeder alone. These able experimenters employed 

 plugs of cotton-wool to filter the air supplied to their in- 

 fusions. Fed with such air, in the great majority of cases 

 the putrescible liquids remained perfectly sweet after 

 boiling. Milk formed a conspicuous exception to the 

 general rule. It putrefied after boiling, though supplied 

 with carefully filtered air. The researches of Schroeder 

 bring us up to the year 1859. 



In that year a book was published which seemed to 

 overturn some of the best established facts of previous 



