26 Milk and Its Products. 
character of the food. Whatever other conditions 
may prevail, the milk is always of a higher color 
where the animals are fed on fresh green forage. 
This has led to the idea that the color of the 
milk is in some way connected with the condition 
of the chlorophyl or green coloring matter of the 
plant. Careno* has suggested that as the chloro- 
phyl undergoes a change when the plant is dried, 
the digestive organs of the animal will have a 
different effect upon it, and so account for the 
difference in color in the milk. 
An albuminoid called lactoprotein has also been 
described in milk. 
Urea to the extent of .001 of 1. per cent 
may also be regarded as a normal constituent of 
milk. 
Variations in quality of milk.— We have already 
seen that the amount of milk secreted may vary 
greatly under the influence of a large number of 
varying conditions. So, too, we find that there 
are a large number of conditions that affect the 
quality of the milk, meaning thereby the relative 
proportion of the various constituents, and particu- 
larly the proportion of fat to other constituents. 
Some of these changes are regular and progressive 
during the period of lactation. Others are due to 
definite causes, and still others occur from time to 
time to which we have as yet been unable to 
ascribe any definite cause. After about the third 
*Milch Zeitung, vol. xxiv. 387. 
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