90 The Conditions of Infusorial Life. 



merits by affirming, that he has never seen the appearance of a 

 proto- organism in water deprived of air, or in water aerated 

 with nitrogen, hydrogen, or carbonic acid ; oxygen alone form- 

 ing an exception. We may here cite a curious observation of 

 M. Pasteur,* on the peculiar fermentation which produces butyric 

 acid. The agent in this process he declares to be an animalcule, 

 which appears in considerable numbers, like small cylindrical 

 rods, isolated, or united in groups, moving in undulations and 

 "pirouettes," and multiplying by fission. They may be trans- 

 planted like yeast, setting up the butyric fermentation in appro- 

 priate substances; and they have this peculiarity, "not only do 

 these infusoria live without air ; but air kills them. Carbonic 

 acid does not affect them.'''' 



The influence of heat and light on the production of infu- 

 soria engaged much of M. Pouched s attention ; and we find him 

 repeating previous experiments, and adding others entirely 

 new. The results he arrived at were, that no animalcules are 

 generated in infusions kept at a temperature below -\- 5° cent. 

 (41° Fahr.) In macerations, kept at a temperature of 12° cent. 

 (54° Fahr.), eight days often elapsed before many adult kolpods 

 appeared, while, at 26° cent. (79° Fahr.), four days sufficed to 

 produce "numerous legions, perfectly developed." He like- 

 wise observed the tendency of different temperatures to develop 

 different species in the same solutions, and came to the con- 

 clusion of Gruithuisen, that from 80° to 96° Fahrenheit was the 

 greatest heat at which infusoria were generated at all. When 

 however they were in existence, they could support extreme 

 changes. Thus, if animalcules living in a liquid at 22° cent. (72° 

 Fahr.), found themselves at the freezing point, in the course of 

 a few minutes, they manifested no inconvenience. In order to 

 test the assertion, that infusoria would revive after being actually 

 frozen, M. Pouch et made several trials, which had the result 

 of showing, that a mass of ice usually contains minute spaces 

 filled with water, which has not congealed, and it is in these 

 that the animalcules live. When however an entire mass was 

 solidified, the larger species perished, and their dead bodies re- 

 mained, while monads and vibrions frequently escaped. Some 

 vibrions he found able to sustain the intense cold of 15° below 

 zero in the centigrade scale, or 27 degrees below the freezing 

 point ofFahrenh.it. 



A moderate intensity of light was observed to be more 

 favourable than an excess of luminosity, and direct sunshine in 

 very hot weather had an injurious effect. White light was the 

 most favourable, then red, then violet, blue, and green, for the 

 production of the protozoa; although microscopic vegetation 

 was affected in an opposite way, green being the most favourable, 



* Comptes Rendus, 25th. February, 1S61. 



