342 
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 
occurring in milk. 
PART II ( 3 ). CHANGES IN MILK BROUGHT ABOUT BY THE ACTION OF 
THE DIGESTIVE 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 glycerine, the milk sugar is likewise converted into 
glucose and galactose by lactase, and the .proteids into simpler and 
more diffusible nitrogen compounds by the proteolytic ferments. 
Chief among these proteids is caseinogen, which, according to Leh- 
mann and Hempel (1), has the following composition: 
Per 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. 
Gly cocoll 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 
Histidin 2. G 
Arginin 4. 84 
Tryptophane 1. 5 
Ammonia , 1.8 
Cystein 0 
Amino valerianic acid - 1 
Glucosamin. 0 
Diamino-trioxy dodecanoic acid 75 
According to this author the absence of glycocoll and the carbo- 
hydrate radical and the relatively high tyrosin and tryptophane 
content of caseinogen render it especially readily digestible. It 
