20 MILK HYGIENE 



inic). The composition of the fat is subject to numerous 

 variations and these are not alone racial peculiarities, 

 for individual traits, the composition of the food and 

 external conditions of life not infrequently influence it. 



Other Substances. Milk contains other substances 

 in very slight quantities : urea, kreatin, kreatinin, leci- 

 thin, cholesterin and citric acid. It is not yet known if 

 these appear in the milk of all animals or whether some 

 of the substances are characteristic of certain animals 

 only. 



Besides these substances, milk contains some inor- 

 ganic salts in solution, which remain after evaporating 

 and burning the milk. The ash consists of lime, potash, 

 sodium, small quantities of magnesia and traces of oxide 

 of iron in combination with phosphoric acid, chlorine 

 and sulphuric acid. The small surplus of basic sub- 

 stances in the ash were in combination with citric acid 

 and, perhaps, with other organic acids. Phosphoric acid 

 and lime exist partly as soluble compounds, partly in 

 combination with casein. A little di- and tri-calcium 

 phosphate are held in solution by the action of the casein 

 and are therefore precipitated with it. The milk of dif- 

 ferent species and sometimes of different individuals, 

 shows a quantitative difference in the ash. 



According to recent investigations, milk, at least 

 cow's milk, always contains a ferment, the so-called 

 galactase (Babcock, Russell), which is capable of slowly 

 peptonizing protein. The significance of this ferment 

 and its composition are wholly unknown to us ; possibly 

 it comes from the breaking down of the leucocyte 

 (Barthel). 



Certain gases occur in the free state in milk. 

 Investigations on this subject have given varying re- 

 sults, in that some investigators have found distinct 

 quantities of oxygen in milk just drawn, others have 



