38 BACTERIOLOGY 



certain characteristics in the growth and multiplication of 

 the elements in this way are more distinctly brought out and 

 that the individual forms are thereby specially distinguished. 



Preparation of peptone bouillon gelatine. The Koch- 

 Loffler peptone bouillon gelatine is that most in use, and is 

 prepared in the following manner : 500 grms. of meat freed 

 from fat are minced up fine, mixed with a litre of water, 

 and allowed to stand for twenty-four hours, after which the 

 mass of meat is squeezed out, the nitrate boiled in a water- 

 bath for three quarters of an hour until all albuminoid 

 bodies are precipitated, and then filtered again. Another 

 method is to place the meat, over which a litre of water has 

 been poured, at once upon the fire, between the flame of 

 which and the vessel a plate of asbestos must be interposed. 

 The broth is made to boil for several hours and then let 

 cool, in order to separate the fat, after which it is filtered 

 and sufficient water poured in to replace that lost by 

 evaporation. 100 grms. gelatine, 10 grins, colourless pep- 

 tone, and 5 grms. common salt are next added to the 

 filtrate, and this mixture is allowed to stand for some time 

 and then heated in the water-bath until all the gelatine is 

 dissolved. In order that the gelatine may be colourless, 

 the solution must not become concentrated while being 

 heated in the water-bath, but from the very commencement 

 as much water must be added, from time to time, as it ap- 

 pears to have lost by evaporation. The reaction of gelatine 

 is always acid, and this is also the case with broth, so that 

 it must be neutralised with a concentrated solution of 

 sodium carbonate or with solution of caustic soda. 



The entire mass is next filtered through a creased filter 

 paper in the hot-water funnel. 1 The creased paper must 

 be moistened with warm water before filtering, as otherwise 



1 [The paper is not folded in the manner usually adopted, but creased in 

 folds radiating from the centre, somewhat like a circular fan ; the piece 



