TYPES OF BACTERIA COMMONLY FOUND IN MILK 285 



Bacterial growth does not, however, entirely cease even at a 

 temperature of o C, as has been shown by the work of Pennington 

 and others. 



The work of St. John and Pennington shows also that 

 bacteria multiply more readily in milk after it has been heated 

 than before. This fact has been shown by a number of authors, 

 reference to which will be found in the paper mentioned. 



The rate of development of bacteria in milk will depend upon 

 the temperature at which the milk is kept on its transit from 

 the farm to the consumer. Moreover, where milk is pasteurised 

 on a large scale, any subsequent contamination will tend to pro- 

 duce a rapid rise in the bacterial content of the milk which has 

 been thus treated. 



There is no direct evidence as to the effect upon infants of 

 feeding them with milk containing a high bacterial content, 

 but the risk of pathogenic organisms is clearly increased when 

 the total number is great. Moreover, it is well known that 

 deleterious results are produced by feeding animals on large numbers 

 of organisms even though these are of harmless types. Milk 

 having a high bacterial content must be regarded as contaminated 

 food, and general experience shows the risk of using such material. 

 The investigations published by Park and Holt, and referred 

 to in detail on pp. 192-3, illustrate this point. 



The remedy for existing contamination in a food material, lies in 

 heating it before it becomes harmful, and this is the usual method em- 

 ployed with milk. The possibility of the presence of toxic substances 

 formed by the bacteria must be considered, but there is comparatively 

 little evidence available on this subject. The only work in regard 

 to the progress of children in relation to the bacterial content of 

 milk appears to be another section of the work of Park and Holt. 

 The work formed a part of the comprehensive investigation under- 

 taken in New York City in the summers of 1901 and 1902. The 

 children were visited in their homes by physicians appointed for 

 the purpose, the method of feeding being noted, together with 

 the progress of the children and the general home conditions. 

 In cases where it was desired to study the effect of certain forms 

 of milk, as in the work about to be described, arrangements were 

 made for the supply of that milk to the people. The experiments 

 are of sufficient interest to quote them somewhat freely. 



Efforts were made to secure comparable conditions in the 

 various groups of children, but the difficulties connected with 

 delivery of milk, etc., rendered it necessary to keep the groupings 

 in different parts of the city. It happened that the children fed 

 on the cheap store milk lived under worse home conditions than 

 those fed on pure bottled milk. The table on the next page shows 

 the figures obtained. 



The authors summarise the results as follows : ' There is nothing 

 in the observations to show that fairly fresh milk from healthy 



