28 
(c) The composition of milk, broth, grape-juice, and lemon juice is as 
follows: 
MILK 
Water 
S7.10 per cent 
Casein and Albumen 
3.40 “ 
• • 
Fat 
3.90 “ 
“ 
Milk Sugar (lactose) 
4.75 “ 
“ 
Ash constituents 
0.75 “ 
•• 
Reaction pH 
MEAT BROTH 
6.S 
Water 
98.70 “ 
“ 
Peptone 
1.00 “ 
«• 
Meat Extract 
0.30 “ 
“ 
Reaction pH 
GRAPE JUICE. 
7.h 
Water 
82.90 “ 
“ 
Sugar (dextrose) 
15.00 “ 
“ 
Tartaric Acid 
1.00 “ 
Soluble Nitrogen 
0.40 “ 
“ 
Ash 
0.70 “ 
•• 
Reaction pH 
LEMON JUICE 
4.50 
Water 
94.30 “ 
“ 
Sugar 
0 20 “ 
“ 
Citric Acid 
500 4 
“ 
Ash 
0.50 “ 
“ 
Reaction pH 
2.20 
What determines the changes and the kinds of organisms causing the 
changes in the above materials? 
( d ) Why does milk undergo an acid fermentation? 
( e ) What is the source of the acid in the lemon and grape juice? 
(0 What kind of change took place in the broth? Why? 
(g) What characteristics of natural organic substances determine 
the possiblity of their decomposition by microorganisms? 
(/?) What relation do these facts bear to agriculture? 
