THE CHEMICAL CONSTITUENTS OF MILK 311 



These equations do not show the varying, but usually con- 

 siderable amounts of glycerine, propionic acid, etc., which are 

 formed at the same time. 



Milk Faults. Red, yellow, and blue colours sometimes 

 develop in milk as a result of the growth of various organisms 

 derived from water, hay-dust, dung, etc. A red colour may 

 also be caused by the presence of blood in the milk, due to the 

 rupture of some of the smaller vessels in the udder. 



Slimy or ropy milk may also be due to the growth of 

 organisms, but the phenomenon is not well understood. The 

 growth of certain bacteria imparts a bitter taste to the milk. 

 More commonly the bitter taste is due to the direct absorption 

 of some bitter substances from the food of the animal, e.g. 

 from turnips, vetches, lupines, etc. Various diseases/ such as 

 tuberculosis, cholera, typhoid, etc., are easily propagated by 

 contaminated milk. 



Preservatives. In order to prevent the souring and other 

 fermentations of milk, various " preservatives " are used. They 

 may be broadly divided into two classes, viz. (i) those which 

 do not hinder fermentation, but merely neutralise the acid as 

 it is formed, and so disguise the effect. Sodium bicarbonate 

 is most commonly used for this purpose, but calcium carbonate 

 (chalk) has also been employed. (2) Antiseptics, which inhibit 

 or retard the action of the bacteria. The commonest are 

 borax or boracic acid, salicylic acid, formalin, and hydrogen 

 peroxide. The first two are not very effective, and are now 

 rarely used. The substance sold under the name of formalin 

 is really a 40 per cent, solution of formic aldehyde. It is said 

 that the addition of 0*05 per cent, of this substance will keep 

 the milk sweet for months. The solution of hydrogen peroxide 

 commonly sold for antiseptic purposes contains about 3 per 

 cent, of that substance. It is very effective, but is considered 

 objectionable, on account of the taste it imparts to the milk. 

 Also, it frequently contains poisonous compounds of barium, 

 arsenic, etc. Apart from this, the substance itself would prove 



1 For further information on these and similar topics the reader should 

 consult Percival's "Agricultural Bacteriology," or other works of that 

 kind 



