The Conditions of Infusorial Life. 87 



vours to show that air, wliicli contains no gernis, water, wliich 

 contains no germs, and a decomposing solid, which contains no 

 germs, may, by mutual contact and influence, give rise to. living 

 forms. Here it may be remarked that the almost inconceivable 

 minuteness of some germs, and the great difficulty of insuring 

 their perfect destruction and exclusion, is quite sufficient to throw 

 a doubt upon the accuracy of many of his experiments, without 

 doing any injustice to him as a skilful manipulator; and 

 although we may fail to detect the precise source of error, we 

 are justified, by another class of experiments, in believing that 

 error did exist. It is important, in the present state of physi- 

 ological science, to deal with these questions inductively ; and 

 if certain experiments appear to prove M. Pouchetfs theory, 

 they can only be fairly met by counter-experiments of the same 

 kind, conducted with greater precautions, or by analogous ex- 

 periments of equal importance, and indicating an opposite con- 

 clusion. How this has been done will be seen hereafter. Let 

 us now select from M. Pouchet's book the most interesting; 

 observations on the conditions of infusorial life. 



It is well known that the fermentations or chemical changes 

 in infusions provide one of the necessary circumstances for the 

 development of infusoria, and as boiling infusions checks this 

 action, it is inimical to the appearance of life. Pom of M. 

 Pouchetfs experiments place this in a striking point of view. 

 Four large vessels were covered by one glass shade, so that 

 all might be exposed to the same influences ; each vessel con- 

 tained 300 grammes* of liquid. The first was filled with water 

 which . had been boiled for fifteen minutes, and twenty-five 

 grammes of hay, which had also submitted to ebullition, and 

 the other three with a different mixture. After three days, 

 during which the four vessels had been exposed to a tempera- 

 ture of 24° centigrade scale (or 75° Fahr.), the first exhibited 

 a slight pellicle and a few vibrions, long and short (vib. granifer 

 and vib. levis). The second vessel, containing water wliich had 

 been boiled, and five grammes of hay which had not been 

 boiled, had a well-formed pellicle, a much larger quantity of the 

 same vibrions, and an abundance of kolpods (K. triticiformis) . 

 The third contained water which had not been boiled, and five 

 grammes of hay that had been subjected to the action of 

 boiling water for a quarter of an hour. This contained the 

 same vibrions as the preceding, more numerous than in the 

 first, and less so than in the second vessel, and also a 

 few of the kolpods. The fourth vase contained water and 

 hay as before, neither having been boiled. Its pellicle was 

 much thicker, its inhabitants the same, but much more nume- 

 rous. In another case a strong decoction of hay was exposed 



*, The gramme is 15 '434 grains troy. 



