52 MILK HYGIENE 



ulent material, the nature of whicli is not definitely 

 established. During this disease, several noticeable 

 changes occur in the milk and it is, therefore, very prob- 

 able that pathological processes take place in the cells 

 of the gland and so an excretion of virus is only to be 

 expected. In other acute diseases, as anthrax, hemor- 

 rhages may occur in the tissues of the udder and the 

 admixture of bacteria from the blood follows naturally. 



The changes in the milk caused by microbes, and par- 

 ticularly by bacteria, which comprise by far the greatest 

 number of micro-organisms of milk, are very numerous. 

 These are most readily studied by working with sterile 

 milk (the best way is to use milk -which was taken from 

 the udder in sterile condition, for milk undergoes quite 

 essential changes when heated) and with pure cultures 

 of bacteria. The most important changes are the 

 following : 



a. The milk is unchanged in appearance, reaction, 

 odor and taste in spite of bacterial growth. 



h. The bacteria form alkali (probably ammonia) ; 

 the reaction grows more and more alkaline and when, 

 after some time, a certain alkalinity is reached, the fat 

 is saponified, the neutral casein-lime compound becomes 

 a base and, as a result of this, the milk is changed to a 

 yellowish translucent, whey-like liquid. 



C. The bacteria split up the lactose, forming acid. 

 The main product of this division is lactic acid, some- 

 times d-lactic acid, sometimes 1-lactic acid, sometimes a 

 mixture of both, i-lactic acid. The reaction may be ex- 

 pressed by this formula: Ci2H220ii+H20^4(C3H603). 

 In fact, however, this process is far more complicated 

 for beside the lactic acids, a number of other com- 

 pounds are formed in small quantity as by-products: 

 alcohol, valeric acid, acetic acid, succinic acid, carbonic 

 acid, etc. After a certain amount of free lactic acid has 



