ENZYMES 21 



Gases. There is no definite evidence of the existence of 

 gases in milk as drawn from the udder, but, during this process, 

 it absorbs the normal constituents of the air. Two analyses of 

 milk gases by Winter Blyth are given in Table VII. 



TABLE VII 

 COMPOSITION OF GASES IN MILK 



Blyth found that, on standing, the oxygen usually dis- 

 appeared in about twenty-four hours and that the carbon dioxide 

 content increased until it finally reached over 95 per cent of the 

 total gases, the residue being nitrogen. 



Enzymes. It has been indubitably proved that fresh milk 

 contains a number of the substances known as enzymes, bodies 

 which are remarkable on account of certain properties which 

 they possess. Small quantities appear to be capable of pro- 

 ducing radical chemical changes without themselves under- 

 going alterations, although their activity is diminished by the 

 transformation products. 



Enzymes are specific in character, i.e., only certain specific 

 enzymes are capable of acting upon certain compounds, and 

 this property has led to the adoption of a nomenclature which 

 classifies the enzyme in accordance with the nature of the com- 

 pound acted upon or the nature of the action produced. For 

 example, the enzyme acting upon amylose is known as amylase, 

 whilst lactase, glucase, and protease, act upon lactose, glucose, 

 and protein, respectively: oxidases and reductases oxidise 

 and reduce, and catalase acts as a catalytic agent. 



Enzymes are thermolabile, have optimum temperatures of 



