ISOLATION OF SPECIFIC PATHOGENES 78a 



red. On cooling, the color should disappear. The 

 change of color adjusts itself slowly; that is, if acid 

 is added, the pink or red color desired may develop 

 immediately but will fade after a few minutes, more 

 acid being then required. 



" The brilliant green should not be added imtil the 

 reaction is adjusted, or, if the agar is kept in stock, 

 it should be added just before pouring the plates. 

 We have also been adding the sugars, m 25 per cent 

 solutions, just before pouring. 



" The most convenient method is to have the agar 

 in bottles of 100 c.c. each, from each of which we 

 make six plates only, as the layer of agar should be 

 thick. 



" After pouring, the plates should be left open till 

 the agar is hardened, and then covered with porous 

 covers to absorb the water of condensation. Unless 

 the plates are absolutely dry, diffusion becomes trouble- 

 some. 



" We have added o.i per cent glucose, which has 

 the effect of markedly increasing the size of the t>-phoid 

 colonies, but has the disadvantage of causing some 

 color to appear in them, especially if they are closely 

 packed. As the typhoid colonies are rather charac- 

 teristic (when glucose is present), this does not as a nde 

 interfere. Furthermore, it gives plenty of material for 

 direct agglutination of the colonies (macroscopic slide 

 method). 



" If one green dye plate is inoculated with the amount 

 that will give discrete colonies on two successive Endo 



