36 CITY MILK SUPPLY 



tested or 12.6 per cent, and tests by the District Health Department 

 upon 51 herds likewise supplying the city detected 160 reacting animals 

 out of 1,095 tested or 15.1 per cent. These figures were regarded as 

 low because the herds tested were believed by their owners to be largely 

 free from the disease. The samples of milk tested by animal inoculation 

 showed that 11 out of 102 dairies or 10.7 per cent, were supplying milk 

 that contained tubercle bacteria. 



The New York investigation of 1909 was undertaken to determine 

 first, what percentage of the milk of New York carried tubercle bacteria; 

 second, what percentage of tubercle bacteria in the milk are of human 

 and what of bovine origin; and third, what effect the infected milk has 

 upon children. The samples were taken from 40- qt. cans in grocery 

 stores, dairies and large milk plants in various quarters of the city and 

 every sample was tested both by microscopical examination and animal 

 inoculation. Out of 105 successful tests 17, or 16.2 per cent., gave posi- 

 tive results. Eight cultures were isolated and studied to determine 

 whether the bacteria were of the human or bovine variety; it was found 

 that one was the former and seven of the latter type. Ten of the 17 

 milk dealers whose milk gave positive tests let their children have the 

 milk to drink raw. These 10 dealers had 18 children, 16 of whom were 

 tested with tuberculin with four reactions. 



Length of Life of Tuberculosis Germs Outside the Body. To deter- 

 mine the length of time tuberculosis germs live outside the animal, 

 many studies have been made. Sunlight and desiccation are the two 

 agents that nature uses most effectively to destroy microbes. Direct 

 sunlight kills tuberculosis germs in a few hours or even in a few minutes 

 when a culture is spread out in a thin film on glazed paper or glass slips. 

 The organisms live 10 or 15 times as long in diffuse as in direct light. 

 There are many difficulties in determining the length of time bacteria 

 will withstand drying and the many bacteriologists that have investigated 

 the subject experimentally have obtained conflicting results. The work 

 that has been published since 1900 seems to indicate that the germs 

 naturally placed will withstand drying for from a week to a couple of 

 months. 



Moore says that tuberculosis germs, expelled in the saliva on pastures 

 where direct sunlight reaches them, soon perish; that in fecal matter 

 where they are somewhat protected from sunlight they will live longer, 

 that in mangers in dark damp stables they will live a considerable time 

 and that such stables are thought to remain infected several months. 



Mode of Infection of the Herd. As to how herds are infected many 

 ways may be conceived but practically only two are important: the 

 disease may be introduced (1) with certain feeds, particularly with skim- 

 milk or whey returned unsterilized from creameries and cheese factories, 

 or (2) by buying the disease through the purchase of diseased stock. 



