34 PRACTICAL BACTERIOLOGY. 



is then added to it, well mixed with it, and the mixture 

 boiled for a few minutes. The coagulated albumen 

 sinks to the bottom of the beaker, carrying with it 

 all the small impurities which were suspended in the 

 fluid, and another filtering is sure to yield a clear 

 preparation. 



The milk is placed at once in the vessels, to be used 

 for the cultivations of the bacteria, and is boiled in 

 them. 



Amongst the solid nutrient media we shall consider 

 the following : nutrient gelatine, nutrient agar-agar, 

 blood serum, and potatoes. 



Nutrient gelatine can be prepared in various ways, 

 and may have various compositions. The kind which 

 is best adapted for most purposes is obtained in the 

 following manner : — The meat-juice is prepared in the 

 same way as for the nutrient bouillon, but 50 to 100 

 grammes of the finest white gelatine are added to it, as 

 well as the ten grammes of peptone and five grammes of 

 common salt. Ordinary commercial gelatine is gener- 

 ally not white enough; if it is used for the prepara- 

 tions, it imparts to them a darkish coloration, which is 

 a great drawback in certain experiments. The gelatine, 

 peptone, and salt are dissolved in the warm liquid by 

 constant stirring; the liquid is then boiled up, neu- 

 tralised in the manner described above, boiled for 

 half an hour, and then filtered. In order to keep the 

 liquid hot, whilst it is being filtered, the hot-water 



