24 ACTION OF AUXETICS AND KINETICS 



select some method for permanent use, and the jelly 

 method gives the most satisfactory results. One 

 special advantage of this method is that the nucleus 

 is always in view, and changes can be seen taking 

 place in it in the living unstained cell (fig. 6). 



Choice of Media for Cultures. For ordinary 

 stock-cultures a 2-per-cent. agar jelly made with 

 distilled water only is used ; the addition of salts is 

 of no advantage, as there is an ample growth of 

 bacteria to supply the amoebae with food without 

 them. Nutrient media are quite unsuitable under 

 ordinary circumstances, as the over - abundant 

 bacterial growth which they bring about is delete- 

 rious to amoebae ; they may, however, be employed 

 with certain pure strains of slow-growing bacteria, 

 or of those which do not produce poisonous sub- 

 stances which are injurious to the amoebae. We 

 have not found agar strained through egg-white 

 an advantage over that filtered through paper or 

 cotton- wool, although Wherry is inclined to think 

 that the ovo-mucoid extracted by the first-named 

 method is favourable to the growth of amoebae. 

 Gelatin media are no use for impure cultures, but 

 with non-liquefying bacteria they serve as a useful 

 test of purity. At last, when we were able to 

 cultivate the amoebae in the absence of living 

 bacteria, we employed a jelly consisting of 2-per- 

 cent, agar two parts and 1 2-per-cent. gelatin one 

 part, because in addition to this being very trans- 

 parent and sterilisable by boiling, it showed any 

 bacterial contamination, for the bacteria caused the 

 gelatin to liquefy. 



In-vitro Staining by the Jelly Method. This 

 consists in placing the amoebae or their cysts on a 



