THEORY OF FERMENTATION 359 



between moulds and bacteria, inasmuch as the presence 

 of a small quantity of acid in the nutritive medium facili- 

 tates the growth and propagation of the former, whilst 

 it is able to prevent the life of bacteria and vibrios? Al- 

 though 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. How greatly they differ 

 in this respect from the diatomacae, for example ! When the 

 vibrio encounters an obstacle it turns, or after assuring 

 itself by some visual effort or other that it cannot over- 

 come it, it retraces its steps. The colpoda undoubted in- 

 fusoria 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 every- 

 where else, how can we avoid believing that they are 

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

 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 king- 

 doms. 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 many respects an unnecessary 

 one. In all the questions which we have discussed, whether 

 we were speaking of fermentation or spontaneous gener- 

 ation, 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 replying " No ; ferment 

 is an organized being, the germ of which is always pres- 

 ent, and the albuminous substance merely serves by its 



