AD DEN DA. 



Page 46, paragraph b, for ' fat " read casein. The fluid has a soap}- feeling, but 

 " saponification " also is probably not the proper term. What actually occurs is a 

 matter for the chemist to determine. The inoculated milk shows no change at first, 

 but gradually becomes intensely alkaline and clears synchronously, without coagula- 

 tion or precipitation. By addition of acids, or concentrated solutions of sodium 

 chloride, copper sulphate, etc., the transparent fluid may now be filled with a white 

 flocculence, which slowly settles to a bulky caseous precipitate, leaving a superna- 

 tant clear, pale whey. It usually requires a month or six weeks for the inoculated 

 milk to become entirely transparent, but a similar transparency may be produced at 

 once in check tubes of milk by adding a few drops of ammonia-water. 



On testing cultures grown for a few days in " nitrate bouillon," as described 

 on p. 63, it happens frequently that there is no nitrite reaction. It is then neces- 

 sary to know whether nitrate is actually present in the bouillon. Usually cultures 

 of Bacillus coli, or some other known nitrate-reducing organism serve this purpose. 

 If such cultures have not been provided, the test for nitrates may be made with 

 dipheuylamiii dissolved in strong sulphuric acid. On addition of a few drops of 

 this reagent there is an immediate, evanescent, deep-blue reaction if nitrates are 

 present. The reagent is prepared by slowly dropping 90 cc. of c. p. sulphuric acid 

 into 10 cc. of pure water, after which i gram of diphenylamin is added, and the 

 solution preserved in a glass-stoppered bottle. 



267 



