218 SCIENTIFIC FEEDING OF ANIMALS 



quantities of urea, lecithine, cholesterine, citric 

 acid, etc. 



When milk is placed under the microscope it is 

 seen to be composed of a clear liquid, in which a 

 great number of tiny drops of fat are present. 

 The fluid form of the nutrients and the finely 

 divided condition (emulsion) of the fat ensure the 

 complete accessibility of the digestive juices to 

 all the constituents of the milk. It is true that the 

 proteins of the milk are acted upon shortly after 

 ingestion by an enzyme in the gastric juice, and 

 curdled, but the curd is in such a form that it offers 

 no resistance to the process of digestion (p. 146). 

 Investigations with sucking calves have also shown 

 that only 2-3% of the ingested dry matter of the 

 milk passes into the faeces (see Part III, Chapter VI). 



When a comparison is made of the composition 

 of the milk of various animals, considerable differ- 

 ences are seen to exist between the quantities of the 

 organic and also the mineral constituents. In 

 cow's milk, for instance, the average composition 

 is 2 -9% casein, 0-5% albumin, 3-4% fat, 4-6% 

 milk sugar, 07% ash, which contains 26% phos- 

 phoric acid. The milk of the mare has 1-3% casein, 

 07% albumin, i-i% fat, 5'9%milk sugar, 0-4% ash, 

 which contains 32% phosphoric acid. From such 

 differences it is easy to see that cow's milk when used 

 as food for the young of other species cannot be 

 as beneficial as the milk of the animal's own mother. 



