STUDIES ON FERMENTATION. 39 



had occasion to remark, a great number of the organisms which 

 would spring into existence of their own accord, if they were 

 allowed sufficient time for germination, are kept back by others 

 of a more rapid development. The truth of this is evident 

 from the fact that we may observe greater variations in the 

 nature and number of species of living organisms, if we divide 

 one infusion amongst several vessels which are immediately 

 closed up again, than if we leave our infusion in contact with an 

 unlimited volume of surrounding air. By this means we expose 

 each portion of the liquid to no other germs than those existing 

 in a state of suspension in the volume of air introduced into the 

 vessels ; and it so frequently happens that we obtain a variety 

 of germs which, coming into contact with a liquid adapted to their 

 nutrition, without having mixed with others, finally multiply 

 there, in consequence of no other organisms of greater activity 

 occurring to impede their slow and laborious propagation. 



The nature of the products resulting from raw infusions — 

 that is, those obtained, without heating, from the maceration 

 of organic substances, such as leaves, fruits, grains, or the organs 

 of plants or animals — is much more varied. The reason of this 

 is that such substances generally carry with thera not only the 

 particles of dust existing in air that is in motion, but also micro- 

 scopic parasites, which find a congenial resting-place on their 

 surface or its vicinity. We may cite a few accurate observations 

 on this point, for the subject is one of great interest. 



If we boil an infusion of hay, and then expose it to contact 

 with the air in a room, all its productions will be derived from 

 such germs as a comparatively still air can carry about ; thus, 

 we shall very rarely find any colpoda in our infusion, for the 

 germs of these infusoria, consisting of rather large cells, can 

 scarcely exist in a state of suspension in motionless air, in spite 

 of their extraordinary diffusion in nature. On the other hand, 

 we almost invariably find colpoda in macerations of raw hay. 

 This difference is easily accounted for ; the particles of dust 

 adhering to the surface of hay, especially that which comes 

 from marshy districts, contain the germ-cells of colpoda in 



