THE MILK SITUATION IN THE DISTRICT OF COLUMBIA. 95 



the lactic-acid organisms, may increase to large numbers and produce toxins 

 and poisonous decomposition products. 



2. The pasteurization of dirty milk, while reducing the bacterial numbers, 

 does not destroy the toxins or other products of bacterial growth. 



3. Careless methods of handling after pasteurization may result in serious 

 contamination of the milk. 



4. Pasteurization may be used simply to cover up dirty milk. It may encour- 

 age dirty methods in production and retard the extension of sanitary super- 

 vision. 



5. Milk which has not been sold may be pasteurized, or even repasteurized, 

 and its faults hidden. 



6. Bacteria may increase more rapidly in. pasteurized milk than in raw milk. 



7. Undesirable changes may be produced by heating, which result in making 

 the milk less digestible, particularly in the case of infants. 



The paper concludes with the statement that commercially pas- 

 teurized milk always sours, because of the development of lactic-acid 

 bacteria which, on account of their high thermal death point, survive 

 pasteurization, and perhaps in some cases because of subsequent in- 

 fection with acid-forming bacteria during the cooling and bottling; 

 that the acid development in an efficiently pasteurized milk is about 

 the same as that in a clean raw milk ; that the " old " taste which 

 sometimes develops is not characteristic of pasteurized milk, but may 

 be noticed as well in clean raw milk when held under similar con- 

 ditions; that the relative proportions of the groups of peptonizing, 

 lactic acid, and alkali or inert bacteria are approximately the same 

 in efficiently pasteurized as in clean raw milk; that the peptonizing 

 bacteria are present in smaller numbers in the inferior grades of 

 commercially pasteurized milk during the first 24 hours after re- 

 ceiving than in raw milk of the same quality; that the number of 

 peptonizers in a good grade of commercially pasteurized milk on the 

 initial count and on succeeding days is approximately the same as 

 in a clean raw milk when held under similar temperature conditions ; 

 that lactic-acid bacteria of high thermal death point are found in 

 milk and may be easily isolated by special methods of procedure, 

 these heat-resisting lactic-acid bacteria playing an important part in 

 pasteurized milk and undoubtedly accounting to a large extent for its 

 ultimate souring; that all milk, whether pasteurized or raw, must 

 necessarily be infected during cooling and bottling by bacteria in the 

 receiving tanks, in the pipes, in the cooler, and in the bottles ; that the 

 low bacterial counts obtained from pasteurized milk in these in- 

 vestigations show that reinfection must have been very small; that 

 it is manifestly unfair to conclude that bacteria increase faster in 

 pasteurized than in raw milk, simply from a comparison of the ratio 

 of bacterial increase, it being evident from the results of this in- 

 vestigation that the bacterial increase in an efficiently pasteurized and 

 a clean raw milk is about the same when the samples of milk are 

 held under similar temperature conditions ; that the " holder " proc- 

 ess of pasteurization is superior to the " flash " process, a tempera- 

 ture of 145 F. (62.8 C.) for 30 minutes appearing to be best adapted 

 for efficient pasteurization; that pasteurized and raw milk should 

 always be bottled and should not be allowed to be sold as " loose " 

 milk from stores ; and that pasteurization should invariably be under 

 the control of competent men who understand the scientific side of the 

 problem. 



One of the chief objections urged against pasteurization is that 

 it promotes carelessness and discourages efforts to produce clean 



