CULTUEE MEDIA 57 



to 100 C., and filtered through " papier Chardin." The 

 liquid is tubed and sterilised at 115 C. for twenty minutes. 

 The yolk is beaten up with ten times its volume of distilled 

 water and a sufficiency of normal caustic soda solution 

 is added to clarify it (about 1 c.c. per 100 c.c.). It is then 

 treated as the egg-white. The authors recommend the 

 use of Martin's broth. 



Peptone water. Add to distilled or tap water 1 to 2 per 

 cent, of Witte's peptone and \ per cent, of common salt, 

 dissolve by heat, make faintly alkaline, steam for one 

 hour and filter. 



For the cholera vibrio it is an advantage to add 1 per 

 cent, instead of J per cent, of common salt (Dunham's 

 solution). 



Beer-wort. Procure beer-wort (preferably unhopped) 

 from the brewery. Allow it to stand in a cool place 

 for twelve hours, filter, and then steam for an hour and 

 filter again. Fill into sterile test-tubes and sterilise. 



Nutrient gelatin. This is prepared in precisely the same 

 manner as peptone beef-broth with the addition of 

 100 grm. of the best " gold label " gelatin (Coignet's) per 

 litre. After the addition of the egg, steam for an hour 

 and then filter through two thicknesses of filter-paper in 

 a hot- water funnel (this is best, but it may be done in the 

 steamer at a low temperature, e.g. 35 C.). Fill into 

 test-tubes and sterilise. After the third steaming the tubes 

 are allowed to solidify, either in the upright or oblique 

 position, according as they are required for stab or surface 

 cultivation. 



In hot summer weather 15 or even 20 per cent, of gelatin (150 grm. 

 or 200 grm. to the litre) are necessary for the product to remain 

 solid, as nutrient gelatin melts at 24 C. or a little under. Pro- 

 longed boiling diminishes and ultimately destroys the gelatinising 

 power of gelatin, so the less it is heated the better. It must not 

 be autoclaved. 



