480 THE POPULAR SCIENCE MONTHLY. 



Schwann then varied his experimental argument, with no alteration in 

 the result. His final conclusion was, that putrefaction is due to decom- 

 positions of organic matter attendant on the multiplication therein of 

 minute organisms. These organisms 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 putrescible liquid from a putrefying one. The 

 sterilized infusion remained perfectly intact. Hence it was not the 

 liquid of the putrefying mass for it 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 subse- 

 quently followed up by Schroeder alone. These able experimenters 

 employed plugs of cotton-wool to filter the air supplied to their infu- 

 sions. Fed with such air, in the great majority of cases the putres- 

 cible 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 Schroe- 

 der 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 investigators. Its title was 

 " Heterogenic," and its author was F. A. Pouchet, Director of the 

 Museum of Natural History at Rouen. Ardent, laborious, learned, 

 full not only of scientific but of metaphysical fervor, he threw his 

 whole energy into the inquiry. Never did a subject require the exer- 

 cise of the cold, critical faculty more than this one calm study in the 

 unraveling of complex phenomena, care in the preparation of experi- 

 ments, care in their execution, skillful variation of conditions, and in- 

 cessant questioning of results, until repetition had placed them beyond 

 doubt or question. To a man of Pouchet's temperament, the subject 

 was full of danger danger not lessened by the theoretic bias with 

 which he approached it. This is revealed by the opening words of 

 his preface : " Lorsque, par la meditation, il fut evident pour moi que 

 la generation spontanee etait encore Tun des moyens qu'emploie la 

 nature pour la reproduction des etres, je m'appliquai a decouvrir par 

 quels proced6s on pouvait parvenir a en mettre les phenomenes en 

 evidence." It is needless to say that such a prepossession required a 

 strong curb. Pouchet repeated the experiments of Schulze and 

 Schwann with results diametrically opposed to theirs. He heaped 

 experiment upon experiment, and argument upon argument, spicing 

 with the sarcasm of the advocate the logic of the man of science. In 



