1 88 



Cultivation of Micro-organisms 



"The first thing to obtain is a standard 'indicator' which will give uniform 

 results. These requirements are best fulfilled by phenolphthalein." 



"The question of the proper reaction of media. for the cultivation of bacteria 

 and the method of obtaining this reaction have' been discussed in a valuable 

 paper by Mr. George W. Fuller, published in the 'Journal of the American Public 

 Health Association,' Oct., 1895, vol. xx, p. 321." 



"Method of determining the degree of reaction of culture-media: For this 

 most important part in the preparation of culture-media, burets graduated into 

 one-tenth c.c. and three solutions are required 



Fig. 43. Buret for titrating media. (From Hiss and Zinsser, "Text-Book of 

 Bacteriology," D. Appleton & Co., Publishers.) 



"i. A 0.5 per cent, solution of commercial phenolphthalein, in 50 per cent, 

 alcohol. 



"2. A solution of sodium hydroxid. 



"3. A solution of hydric chlorid. 

 20 



"Solutions 2 and 3 must be accurately made and must correspond with the 

 normal solutions soon to be referred to. 



"Solutions of sodium hydroxid are prone to deterioration from the absorption 

 of carbon dioxid and the consequent formation of sodium carbonate. To pre- 

 vent as much as possible this change, it is well to place in the bottle containing 

 the stock solution a small amount of calcium hydroxid, while the air entering the 

 burets or the supply bottles should be made to pass through a U-tube containing 

 caustic soda, to extract from it the carbon dioxid." 



"The medium to be tested, all ingredients being dissolved, is brought to the 



