ILLINOIS STATE DAIRYMEN'S ASSOCIATION. 143 



intended for consumption, and if they could be kept out the 

 milk would not change. But on account of their minute 

 size and omnipresence, this is a practical impossibility, and the 

 dairyman is compelled to depend upon one or both of two 

 resources: (i) to allow as few as possible to enter the milk, 

 and (2) to allow them to increase as little as possible after they 

 have entered the milk. There are several ways of checking or 

 entirely preventing the growth of bacteria, but only a few are 

 adapted to a food product such as milk. Various chemicals 

 are sometimes added to milk but while a few advo-. 

 cate their use the weight of opinion is against them. The most 

 common so-called preservatives contain salicylic acid, boric 

 acid, borax or formaldehyde, which are not regarded as poisons 

 but may have an injurious effect when taken in the system 

 in regular small doses. Their antiseptic or germicide 

 qualities may easily interfere with the natural processes of diges- 

 tion and the danger becomes greater because of their supposed 

 harmlessness and the use of larger amounts of them than is 

 actually necessary for the purpose intended. 



The development of bacteria is also checked by extremes of 

 temperature and the use of heat or cold for this pupose is 

 perfectly safe. It is well known how quickly milk spoils 

 in a warm place, and how long it may be kept sweet at a low 

 temperature. At ninety degrees Fahrenheit the germs grow 

 with great rapidity and the rate of their increase decreases 

 with a decrease of temperature, — at fifty degrees Fahrenheit 

 they are quite inactive, but at this and considerably lower 

 degrees of heat they retain life and some forms continue to 

 multiply. It has been shown that at ninety-three degrees 

 Fahrenheit certain germs may increase in numbers, in four 

 hours, more than 200 fold, while at fifty-five degrees Fahren- 

 heit they would increase only about eight fold. Up to a certain 

 point the higher temperatures have the same effect as cold, i. e. 

 make the germs inactive. But when the heat is raised to 125 

 degrees Fahrenheit some are killed, those not harmed by this 

 temperature are destroyed by greater heat. A sufBcieut tem- 

 perature to kill almost all of the growing forms found in milk is 



