306 MILK 



bacteria which multiply in remnants of milk and then increase 

 the germ content of the product. 



Besides reduction of germ content of the milk, other advan- 

 tages may be derived from the use of milking machines. One of 

 these is the reduction of help necessary to carry on milk produc- 

 tion. Farm help is notoriously difficult to obtain, and through 

 scarcity of help the dairy industry has not developed to a desir- 

 able degree. Another advantage lies in the fact that the chances 

 of contaminating milk with pathogenic bacteria from the milker 

 are materially reduced by the aid of milking machines, since the 

 direct contact of human beings is largely excluded. 



The idea of substituting machines for milkers is not by any 

 means of recent origin. Perhaps the earliest attempt to facilitate 

 milking was by introducing straws through the teats into the cis- 

 tern, thus opening the sphincter muscle and allowing the milk 

 to flow from the udder. This method, however, is objectionable 

 because of the contamination from the straw and the possibility 

 of irritating or injuring the tissues. Inventors first occupied 

 themselves with designing milking machines in the decade com- 

 mencing with 1870. Martiny, quoted by Lane, knew of 29 dif- 

 ferent machines that had been patented or mentioned in the 

 literature between 1877 to 1899. In the United States 127 

 patents on milking machines or separate parts thereof were 

 applied for during the period from 1872-1905. But few machines 

 survived actual tests, and it is only within very recent years that 

 the milking machine has become an efficient factor in milk produc- 

 tion. 



Three principles have been applied in designing milking 

 machines, namely: 1, introduction of a milk tube into the cistern; 

 2, pressure applied to the base of the teat where it is attached to 

 the udder; 3, suction. The third principle has proved* the only 

 successful one, as by its means the natural sucking of the calf 

 can be imitated. In machines constructed on this principle the 

 teat is placed in a cup from which the air can be exhausted by 

 means of a pump either a hand-pump, a foot-pump, or a vacuum 

 created by machinery. The best modern machines alternate 

 sucking and pressure by inflowing air, thus creating pulsations in 

 imitation of the sucking of calves. 



Several difficulties presented themselves when machines were 

 first put into practical use. The difficulties have been success- 

 fully overcome, in a measure at least, so that milking machines 

 of modern type actually do the work demanded of them. One of 

 the difficulties was found in proper cleaning of the machine after 

 use. Some parts of the machine are made of rubber, and this is 

 notoriously difficult to sterilize without injuring the material. 



