THE PREPARATION OF CULTURE MEDIA 9 



process of gelatine-plate cultivation, which has been the 

 means of separation and individualisation of so many 

 micro-organisms, and to which the science of bacterio- 

 logy is so largely indebted. 



It was, of course, essential that the culture medium 

 employed should be of such composition as to afford 

 food material for the largest number of micro-organisms, 

 and Koch, after numerous experiments, found that a 

 mixture of gelatine and broth gave the best results for 

 general purposes. The original recipe recommended 

 by Koch is, with a few modifications, that which is 

 still in use. 



In all investigations connected with micro-organisms 

 it must be always borne in mind that all our surround- 

 ings are more or less infested with living forms of the 

 same order as those with which we are dealing, and it 

 becomes, therefore, of paramount importance that every 

 operation should be conducted in such a way as to pre- 

 clude the possibility, or at any rate reduce to a mini- 

 mum the chance, of introducing micro-organisms from 

 foreign sources. The precautions to be taken cannot 

 be too scrupulous or painstaking, and if in the descrip- 

 tion of the various bacteriological processes too much 

 emphasis may appear to have been laid upon the 

 dangers arising from contamination through imper- 

 fectly sterilised vessels &c., the student must re- 

 member that by neglecting even the most trivial of 

 such precautions he may very possibly afterwards dis- 

 cover that the whole of his labour has been rendered 

 worthless, and that to begin de novo is his only alter- 

 native. 



Preparation of gelatine-peptone. — The preparation 

 of gelatine -peptone, which is in many respects the most 

 important of all the culture media, may be best carried 

 out in the following manner : — A pound of beef, as free 



