296 FRAGMENTS OF SCIENCE. 



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 steril- 

 ised putrescible liquid from a putrefying one. The 

 sterilised infusion remained perfectly intact. Hence 

 it was not the liquid of the putrefying mass for that 

 could freely diffuse through the membrane but some- 

 thing contained in the liquid, and which was stopped 

 by the membrane, that caused the putrefaction. In 

 1854 Schroeder and Von Dusch struck into this en- 

 quiry, which was subsequently followed up by Schroe- 

 der 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 

 investigators. Its title was Heterogenie, and its author 

 was F. A. Pouchet, Director of the Museum of Natural 

 History at Eouen. Ardent, laborious, learned, full not 

 only of scientific but of metaphysical fervour, he threw 

 his whole energy into the enquiry. Never did a subject 

 require the exercise of the cold critical faculty more 

 than this one calm study in the unravelling of com- 

 plex phenomena, care in the preparation of experiments, 

 care in their execution, skilful variation of conditions, 

 and incessant 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 



