92 CHEMICAL EXAMINATION 



placed and to these are added 0.1, 0.2, 0.3 up to 1 c.cm. of a 1 

 per cent solution of soluble starch prepared by boiling with dis- 

 tilled water and cooling. After shaking, the tubes are placed 

 in a bath at 43°-45° C. for one hour and then rapidly cooled. 

 To each is added 1 c.cm. of a solution of iodine in potassium 

 iodide (1 grm. iodine, and 2 grms. potassium iodide in 300 c.cms. 

 of water), and the colour noted immediately after shaking. 

 The recording of the tints admits of no delay, as the colours 

 rapidly fade and all the tubes may regain their original shades. 

 A yellow tint indicates total conversion of the starch to sugar, 

 and a blue one unchanged starch: the correct reading is where 

 the yellow just commences to take on a greyish tint. With 

 normal fresh milk this will usually be found between the third 

 and fifth tubes. The indications of this test are similar to 

 those of the catalase test, both being based on the quantity of 

 cellular elements. 



Galactase. The Babcock and Russell method is probably 

 the most reliable for the estimation of this ferment, but the time 

 required for its execution is so long that it is never carried out 

 in routine examinations. The milk is incubated at blood heat 

 for 53 days with the addition of sufficient thymol to prevent 

 bacterial development and an estimation of the soluble nitro- 

 gen then made. The difference between this result and that 

 originally present indicates the amount produced by the enzyme 

 activity. This is usually less than 1 per cent per day. 



BIBLIOGRAPHY 



1. Lythgoe. Jour. Ind. and Eng. Chem., 1914, 6, 906. 



2. Leonard. Analyst. 1896,21,157. 



3. Richmond. Dairy Chemistry. London, 1914, 186. 



4. Shrewsbury and Knapp. Analyst. 1909, 34, 12. 



5. Thomson. Analyst. 1903, 28, 184. 



6. Stoke. Analyst. 1897, 22, 320. 



