TIME AND TEMPERATURE 191 



exceed 500,000 per c.c* In summer the writer has found as many as 

 4,000,000 organisms per c.c. in fresh London milk obtained at first- 

 rate milkshops.-]- 



There is no standard or uniformity in the numerical estimation 

 of bacteria in milk. A host of observers have recorded widely- 

 varying returns due to the widely-varying circumstances under 

 which the milk has been collected, removed, stored, and examined, 

 and due also to the two dominating influences of time and tempera- 

 ture. ISTor is it possible to establish any standard which may be 

 accepted as a normal or healthy number of bacteria, as is done in 

 water examination. Bitter has suggested 50,000 micro-organisms 

 per c.c. as a maximum limit for milk intended for human consump- 

 tion, but actual experience shows that, at present at all events, such 

 standards are impracticable. 



Owing to differences of nomenclature and classification, in addition 

 to differences in mode of examination, at present existing in various 

 countries, it is impossible to state even approximately how many 

 bacteria, and how many species of bacteria, have been isolated from 

 milk. Until some common international standard is established, 

 mathematical computations are practically worthless. They are need- 

 lessly alarming and sensational. And it should be remembered that 

 great reliance cannot be placed upon these numerical estimations, for 

 they vary from day to day, and even hour to hour. Furthermore, vast 

 numbers of bacteria are economic in the best sense of the term, and 

 the bacteria of milk are chiefly those of a fermentative kind, and 

 not disease-producers. J 



The effects of time and temperature upon the bacteria of milk do 

 not only concern the numbers of organisms present. As long ago as 

 1897 DeMpine showed that toxicity of milk was increased by a rise 

 in temperature, and this is as we should expect, for it stands to 

 reason that conditions favourable to the multiplication of bacteria in 

 milk must of necessity tend to increase the products of bacteria in 

 milk, and is likely to increase its virulence. § 



The following tables summarise the more detailed figures given 

 in 1897, and in which the effects which length of keeping and 

 of temperature have upon the noxious effects of the milk are 

 indicated. 



* Brit. Med. Jour., 1895, ii., p. 322. 



t Report on Milk Supph/ of Finsbury, 1903. 



J At the same time it is important to remember that comparative series of 

 estimations as to the number of bacteria per c.c. in milk may be of value as 

 indication of unclean dairying. Leighton of Montclair, U.S.A., has shown that 

 numbers increase in direct proportion to unclean management. See The Milk 

 Supply of Two Hund/red Cities and Towns (Alvord & Pearson), U.S. Dep. of 

 Agriculture, Bull. 46, 1903, p. 117. 



§ Jour, of Comp. Path, and Therapeutics, 1897. 



