1900.] on Symbiosis and Symbiotic Fermentation. 269 



their metabolic processes are not at present understood. Probably 

 when all is known we shall find this is the result of the association, 

 but at present it cannot be said to be established. We must sub- 

 stitute for it in connection with fermentation the idea of power in 

 particular directions possessed by the conjoint organisms, which is 

 not exhibited by either symbiont separately. 



We must guard ourselves still further. There are many fermen- 

 tative processes carried on by microbes in which many such organisms 

 take part simultaneously or successively. Prominent among these 

 we have the phenomena of putrefaction. In this process many 

 organisms take part, some decomposing the original material, for 

 instance, meat ; others attacking the products of the activity of the 

 first, and so on. It is evident that there is here a very great com- 

 plexity, and many of the organisms benefit from, and are indeed 

 dependent upon the activity of the others. But there is at the same 

 time a conspicuous independence among them, and many of them 

 would not be seriously missed if they should not happen to be 

 present. We may rather compare such a series of actions with the 

 struggle for existence which is exemplified by a number of plants 

 growing together in a somewhat confined area, and competing there- 

 fore for the advantages which the environment presents. 



Nor does a true symbiotic fermentation arise in the case of two 

 organisms which live together, one being fed by the materials which 

 the first produces. A curious case is known in which three microbes 

 have been found together, of which one, Bacillus ramosus, decom- 

 poses proteid or gelatinous matters, setting free ammonia ; the second, 

 Nitrosomonas, converts the ammonia into nitrites, or salts of nitrous 

 acid ; the third, Nitrobacter, forms nitric acid or its compounds from 

 this. These are consecutive fermentations and can only go on in 

 the order named, so long as all three organisms are present. They 

 apparently do not influence each other in any way apart from making 

 their particular products; Nitrosomonas will make nitrous acid from 

 ammonia if it is supplied to it from any other source than the activity 

 of the Bacillus, and is, therefore, not dependent upon the presence 

 of the latter as such. The Nitrobacter is to the same extent inde- 

 pendent of the Nitrosomonas. True symbiotic fermentation involves 

 a much closer relationship between the organisms which take part 

 in it, and the general reactions incident to their associated life are 

 much more complex, the influence of one organism upon the other 

 modifying considerably the course of action of each. 



The first of these cases of symbiosis which may be noticed is the 

 fermentation set up by the so-called Kephir, which produces an 

 aerated beverage largely used in the Caucasus. The Kephir exists 

 in the form of, say, somewhat translucent lumps, which swell some- 

 what in water ; they are known as Kephir grains. 



When examined carefully these lumps are found to be composed 

 of three separate organisms which can, by the usual culture methods, 

 be separated from each other. The first of these is known as Bis- 



