566 FRAGMENTS 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 1 
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 
