348 
author has shown that the reductases of milk are different from the 
catalase and superoxidase of milk and separable from these, the latter 
being soluble in water and salt solution, the former not. In recent 
communications Seligmann (45) points out that the reductases and 
peroxidases of cow’s milk are not indentical. According to this 
author all processes of reduction occurring in fresh and sour milk are 
due to the action of bacteria and not to unorganized ferments. 
Cathcart (46) has also made a study of the reduction of Schar- 
dinger’s reagent by fresh milk. According to this author the reduc- 
tion of the coloring matter is due to the presence of a catalase which 
is readily destroyed by heat. Our knowledge, therefore, of the 
reductases of milk is at present very limited, and we are not as yet 
in a position to say whether they are responsible for any of the 
changes ordinarily occurring in milk. 
Part II. — (3) Changes in Milk Brought About by the Action of the Digest- 
ive Ferments — The Rennin Coagulation of Milk. 
The composition of milk is profoundly altered during the process 
of digestion through the action of the digestive ferments. In the 
stomach and intestine the fat is hydrolysed by lipase, giving rise to 
fatty acids and glycerin, the milk sugar is converted into glucose 
and galactose by lactase, and the proteids into simpler and more dis- 
fusible nitrogen compounds by the proteolytic ferments. Chief 
among these proteids is caseinogen, which, according to Lehmann and 
Hempel (1), has the following composition: 
Ter cent. 
Carbon 54. 
Hydrogen 7. 04 
Nitrogen 15. 6 
Sulphur . 771 
Phosphorus . . 847 
The following, according to Mann (2), are the principal dissocia- 
tion products which have been isolated from caseinogen by hydro- 
lytic cleavage : 
Per cent. 
Glycocoll 0 
Alanin . 9 
Leucin 10. 5 
Phenylalanin 3. 2 
Alpha-pyrrolidin carboxylic acid 3.2 
Glutaminic acid 10. 7 
Aspartic acid 1. 2 
Cystin . 065 
Serin — . 43 
Oxy-alpha-pyrrolidin carboxylic acid . 25 
Tyrosin 4. 5 
Lysin 5. 8 
