170 CLASSIFICATION OF THE MICRO-ORGANISMS. 



ences in the structure of the individual cells, can be 

 recognised ; nor can any marked differences be made out 

 in the process of fructification, and yet it is that process 

 which furnishes the most important principle of classifi- 

 cation in other plants and in the higher fungi. In view 

 of the extremely numerous species of bacteria which are 

 already known, and the number of which is rapidly 

 increasing, an enumeration and classification of these 

 organisms appears to be indispensable, in order that we 

 may at least be able to obtain a general view of the 

 known species, to settle the identity of any species 

 which may in future come under observation, and to 

 include new species in the system of classification. This 

 Necessity for necessity for a definite classification, and for a key for 

 claSoSa tne diagnosis of the bacteria, is so great, that in view of 

 of bacteria, the impossibility of forming a classification on the 

 ordinary scientific principles, we must for the present 

 put up with some kind of systematic division, although 

 the principle of the classification may not be founded on 

 the developmental history, nor have analogies in the 

 other departments of botany. Just as in the first begin- 

 nings of a botanical classification any striking external 

 characters which were of use for diagnosis were employed 

 as aids for the distinction and classification of the plants, 

 so we must in the present state of our knowledge with 

 regard to bacteria employ as means of distinction any 

 properties of the bacteria, their morphological and 

 biological characters, their external form, their mode of 

 growth on certain nutrient substrata, their relation 

 to oxygen, their behaviour with regard to stains, &c., 

 provided that these properties are constant and cha- 

 racteristic for the individual species, and enable us to 

 distinguish them readily. We may hope that with the 

 advances in our optical means, and with the further know- 

 ledge of the processes of fructification, we may gra- 

 dually obtain for the bacteria a groundwork on which a 

 true classification can be built, and we must therefore 

 thoroughly realise the provisional character of our 

 present attempts at classification. But to abstain 

 entirely from these attempts would be in the highest 



