TYPES OF BACTERIA COMMONLY FOUND IN MILK 287 



' On the other hand, it is possible that certain varieties of bacteria 

 may, under conditions that are unsanitary, find entrance to milk 

 and survive moderate heat or may develop poisonous products 

 resistant to heat in sufficient amount to be harmful, even when 

 they have accumulated to less than 200,000 per c.c. 



'Turning now to the results of feeding with milk which has 

 been heated and which before sterilisation contained from 1,000,000 

 to 25,000,000 bacteria per c.c., averaging about 15,000,000, though 

 obtained from healthy cows living under fairly decent conditions 

 and kept moderately cool in transit, we find a distinct increase 

 in the amount of diarrheal diseases. Though it is probable that 

 the excessive amount of diarrhoea in this group of children was due 

 to bacterial changes which were not neutralised by heat or to living 

 bacteria which were not killed, yet it is only fair to consider that 

 the difference was not very great, and that the infants of this group 

 were under surroundings not quite as good as those on the purer 

 milk. 



' Finally, we come in this comparison to the infants who received 

 the cheap store milk pasteurised. This milk had frequently to be 

 returned because it curdled when boiled, and contained, according 

 to the weather, from 4,000,000 to 200,000,000 bacteria per c.c. 

 In these infants the worst results were seen. This is shown not 

 only by the death-rate, but by the amount and the severity of the 

 diarrheal diseases, and the general appearance of the children as 

 noted by the physicians. Although the average number of bacteria 

 in the milk received by this group is higher than that received by 

 the previous group, the difference in results between this group 

 and the previous one can hardly be explained by the difference in 

 the number of bacteria. The varieties of bacteria met with in 

 this milk were more numerous than in the better milk, but we 

 were unable to prove that they were more dangerous. Probably 

 the higher temperature at which the milk was kept in transit and 

 the longer interval between milking and its use allowed more toxic 

 bacterial products to accumulate.' 



It has been shown in preceding chapters that it is practically im- 

 possible to obtain milk which can be guaranteed free from germs of 

 disease. The conditions under which 'certified' milk is produced 

 could hardly be made stricter, and yet virulent streptococci and 

 tubercle bacilli have been found in this milk. 1 The remedy can only 

 be found in heating milk before use, and it becomes important to 

 consider the temperature at which the more important organisms 

 liable to be present in milk are destroyed. 



On the Thermal Death-points of Micro-organisms in Milk. 

 Under this heading it will be necessary to consider the temperature 

 at which special organisms of pathogenic type are destroyed, and also 

 the general effect of different temperatures upon the large bacterial 



1 Cp. p. 249 and footnote p. 252. 



