COMPOSITION OF MILK AND EGGS. 257 



ments performed for the purpose, and is illustrated by the 

 composition of the food prepared by nature, as the exclu- 

 sive source of nourishment to the young of Mammalia, 

 namely, milk. 



COMPOSITION OF MILK. 



Human. Cows. 



Water 890 858 



Solids no 142 



1,000 1,000 



Casein 35 68 



Butter 25 38 



Sugar (with extractives) 48 30 



Salts . 2 , 6 



no 142 



In milk, as will be seen from the preceding table, the 

 albuminous group of aliments is represented by the casein, 

 the oleaginous by the butter, the aqueous by the water, 

 the saccharine by the sugar of milk. Among the salts of 

 milk are likewise phosphate of lime, alkaline and other 

 salts, and a trace of iron ; so that it may be briefly said 

 to include all the substances which the tissues of the 

 growing animal need for their nutrition, and which are 

 required for the production of animal heat. 



The yelk and albumen of eggs are in the same relation as 

 food for the embryoes of oviparous animals, that milk is to 

 the young of Mammalia, and afford another example of 

 mixed food being provided as the most perfect nutrition. 



COMPOSITION OF HENS' EGGS. 



White. Yelk. 



Water 80*0 5373 



Albumen .... 15-5 17-47 



Mucus ..... 4-5 Yellow Oil . . 2875 



Salts 4-0 6.0 



The experiments illustrating the same principle have 

 been chiefly performed by Magendie. Dogs were fed 

 exclusively on sugar and distilled water. During the first 

 seven or eight days they were brisk and active, and took 



