STUDIES ON PER MENTATION. • 313 



be a very great and natural difference between moulds and 

 bacteria, inasmuch as the presence of a small quantity of acid 

 in the nutritive medium facilitates the growth and propagation 

 of the former, whilst it is able to prevent the life of bacteria 

 and vibrios ? Although, as is well known, movement is not an 

 exclusive characteristic of animals, yet we have always been 

 inclined to regard vibrios as animals, on account of the peculiar 

 character of their movements, llow greatly they differ in this 

 respect from the diatomacse, for example ! When the vibrio 

 encounters an obstacle it turns, or after having assured itself 

 by some visual effort or other that it cannot Overcome it, it 

 retraces its steps. The colpoda — undoubted infusoria — behave 

 in an exactly similar manner. It is true one may argue that 

 the zoospores of certain cryptogamia exhibit similar movements; 

 but do not these zoospores possess as much of an animal nature 

 as do the spermatozoa ? As far as bacteria are concerned, when, 

 as already remarked, we see them crowd round a bubble of air 

 in a liquid to prolong their life, oxygen having failed them 

 everywhere else, how can we avoid believing that they are 

 animated by an instinct for life, of the same kind as that which 

 we find in animals. M. Robin seems to us to be wrong in 

 supposing that it is possible to draw any absolute line of 

 separation between the animal and vegetable kingdoms. The 

 settlement of this line, however, we repeat again, no matter 

 what it may be, has no serious bearing upon the questions that 

 have been the subject of our researches. 



In like manner the difficulty which M. Robin has raised in 

 objecting to the employment of the word germ, when we cannot 

 specify whether the nature of that germ is animal or vegetable, 

 is in manj;- respects an unnecessary one. In all the questions 

 which we have discussed, whether we were speaking of fer- 

 mentation or spontaneous generation, the word germ has been 

 used in the sense of origin of living organism. If Liebig, for 

 example, said of an albuminous substance that it gave birth to 

 ferment, could we contradict him more plainly than by reply- 

 ing : " No ; ferment is an organized being, the germ of which 



