18 CITY MILK SUPPLY 



sequently he avoids milks affected by them. They often cause producers 

 much annoyance and some loss. 



Bacteria of class 4 are unimportant. It is different with the germs 

 of class 5. These disease-producing organisms effect no changes in 

 milk that would warn the consumer of their presence. When they are 

 considered on the basis of the frequency with which they occur in milk 

 they are not impressive, but when thought of in relation to the havoc 

 they have wreaked on customers, the worry and monetary burdens they 

 have imposed on the dairy industry and the financial loss and ruin they 

 have caused dairymen their consequence becomes momentous. In 

 times bygone the very lack of knowledge of pathogenic organisms was 

 a contributive factor to the loss. Happily, this handicap has been all 

 but removed and effective means of protecting the industry and populace 

 from ravages of this sort are indicated. 



Stages in the Bacterial Decomposition of Milk. The highest grades 

 of milk may contain few bacteria other than the udder types but as milk 

 is ordinarily produced for the market it contains a mixed and numerous 

 flora, the subsequent development of which, as Hastings and others 

 have shown, is determined by a number of factors, important among 

 which are the character and amount of the initial seeding and the tem- 

 perature at which the milk is held. The marked tendency of the lactic 

 acid bacteria to outstrip other forms at temperatures between 50 and 

 67.5F. normally causes a sequence of changes in which there are four 

 principal stages. 



First Stage. The first of these is known as the germicidal stage and 

 lasts for only a short time after the milk is drawn from the udder. Bac- 

 terial counts made at frequent intervals during the first few hours, not 

 over 24, show progressively fewer colonies. There is much difference 

 of opinion among bacteriologists concerning the nature of the phe- 

 nomenon. Some would account for the decrease in numbers on the ground 

 that, though milk is a favorable culture medium for many germs, it is 

 not for all, and consequently those for which it is unsuited die off. Others 

 believe that milk, like the blood and many body fluids, has bactericidal 

 power, though they admit it is weak and soon lost. Rosenau and others 

 believe that the force is not bactericidal but agglutinative; that the 

 bacteria are not killed but are gathered in clumps from which, on 

 the plates, single colonies arise, instead of many as there would if the 

 clumps dispersed. 



All are agreed that for a short time after milk is drawn there is a 

 period wherein the number of germs does not increase but rather tends 

 to fall off. It seems that at high temperature, 98F. for instance, the 

 action is marked but is over in 8 to 10 hr.; at low temperatures the action 

 is not so decided but is more prolonged. The power is lost in 24 hr. or 

 if the newly drawn milk is heated to 176F. This latter fact has been 



