BY OSCAR KATZ. PH.D., M.A. 909 



qua 7i07i — in a liquid state, and having a temperature at any rate 

 not higher than blood-heat, is mixed with whatever it is desired- 

 to test for micro-organisms. In our case, a definite quantity of 

 water is well distributed in a certain quantity of nutrient gelatine 

 in a test-tube, and the still liquid mixture is then, with the adoption 

 of due precautions, of course, transferred to and spread on sterilised 

 glass-plates, which, after sufficient solidification of the layer of 

 gelatine has taken place, are placed in a convenient form of 

 damp chamber, and therein subjected to temperatures not exceeding 

 25° C. (77° F.), for a certain period. The great advantages of this 

 mode of carrying on bateriological examinations are, in the main : — 



(1.) The modus operandi is extremely simple and free from 

 the concomitant complications of other methods regarding bac- 

 teriology. 



(2.) The whole of the germs in the sample of water, or whatever 

 it may be operated upon in the described manner, are deposited 

 all at once on the culture-plates ; they become, each of them, fixed 

 to a separate spot in or on the solidifying gelatine. Here those 

 capable of development in the gelatine — most of the Schizomycetes 

 are — go to form groups or colonies which are not all alike, bat 

 according to the specifically different germs from which they ori- 

 ginate, differ from one another, generally even to the naked eye. 

 In these colonies or vegetations the bacterial species are distinguish- 

 able from one another, just in the same way as " a number of 

 birds in their flights, or socially living ants in their wanderings." 



(3.) From these colonies inoculations on or into various nutritive 

 media for the purpose of obtaining pure cultivations, can be easily 

 and successfully carried out. 



On the other hand, Koch's method of gelatine-plate-cultivation 

 for the bacteriological investigation of water, is not altogether 

 devoid of some sources of error, which seem to be mainly these : — 



(1.) There are a few groups of bacteria which refuse to grow at 

 all in nutrient gelatine, or, at least, within the limits of tempera- 

 ture for solid gelatine. Parasitic species especially, e.g. Bacillus 

 tuberculosis (Koch), will not be found to multiply under this 

 treatment, nor will the forms which are grouped together under the 



