MICKO-ORGANISMS IN MILK 307 



Next to this the greatest difficulty experienced has been proper 

 construction of the teat cups. The size of teats varies greatly 

 not only in different animals but also in the same animal accord- 

 ing to the stage of the lactation period. To meet this condition 

 it was formerly required to have a number of cups available. 

 As a consequence changes frequently had to be made after the 

 cups had been sterihzed, thus exposing them to renewed contamina- 

 tion. By accident or carelessness cups might drop and become 

 contaminated with filth from the floor. 



A third, by no means unimportant, difficulty was the neces- 

 sity of accustoming the cows to the use of the machine. The 

 suction power must be properly regulated, otherwise injury to 

 the teat may result, and the animal must get used to the clicking 

 of the machine caused by the alternation of sucking and pressure. 



Finally, the problem arose whether the machine would exert 

 an influence on milk secretion and decrease the amount of the 

 product and perhaps abbreviate the lactation period. 



These problems have been investigated by a number of au- 

 thorities, and it can be stated that the milking machine has 

 emerged from the experimental period and that means have been 

 found for overcoming many difficulties in large measure. Im- 

 provements have been made rapidly since scientific investigation 

 has shown where the machine was at fault, and it is expected 

 that within a short time further improvements will be made, so 

 that the milking machine will be useful even in the hands of un- 

 trained men. 



The results of using milking machines in earlier periods were 

 rather discouraging. Harrison in 1899, working with the "This- 

 tle" machine, found that the machine-drawn milk had 141,616 

 bacteria per cubic centimeter in the morning's product and 

 165,033 in the evening milk. Hand-drawn milk had but 10,619 

 in the morning's product and 12,890 in the evening milk. The 

 hand-drawn milk had, therefore, about one-fourteenth the num- 

 ber of bacteria that machine-drawn milk contained. 



Later investigations, however, have given more encouraging 

 results. Hastings and Hoffmann found that machine-drawn milk 

 contained no more bacteria than hand-drawn, and this result 

 was obtained when operations were carried on in a barn which 

 was kept in good condition, but not in a scrupulously clean con- 

 dition, such as prevails in certified milk barns. Under more 

 ordinary conditions the outcome of the experiments would prob- 

 ably have been decidedly in favor of the machine. 



An exhaustive study was made by Stocking and Mason in 

 1907. The authors found that the method of cleaning the ma- 

 chine was of paramount importance in producing results. Ma- 



