GEORGE W. PUTNAM 433 



For example, North' and collaborating scientists reported that in a series of tests in 

 which milk was heated in a barrel heater and the temperature reduced slightly in a 

 tubular heater prior to discharging the milk into a holder, all samples from the out- 

 let of the second heater, which had been heated to a maximum temperature of 150° F. 

 or above, showed destruction of tubercle bacilli in artificially infected milk. 



The electrical method of flash pasteurization (see Fig. 5), using hot treated milk to 

 heat raw milk to 1 20° F. by means of a regenerator, and electricity to heat from 1 20° to 

 160° F., is being offered as the equivalent of pasteurization by the holding method. 

 Many health ofiiicers are faced with the problem as to whether or not to accept it as such. 

 Numerous tests have been made on this process in various stages of its development 

 in the last twenty years. Many of these have not been reported in hterature. In 1920 

 Beattie and Lewis' reported to the Medical Research Committee of Great Britain 

 that the process destroyed tubercle bacilH satisfactorily at 63°-64° C. (i45.4°-i47.2° 

 F.) Recently Prescott reported^ that tests made under his direction showed that this 

 electrical method of treating milk destroyed tubercle bacilli satisfactorily when oper- 

 ated at 160° F. On the other hand, Irwin, Haythorn, and Conover,^ testing a com- 

 mercial unit in Pittsburgh, Pennsylvania, reported on April 13, 1926, that four out 

 of twenty-eight guinea pigs injected with portions of samples of milk, artificially in- 

 fected and then treated by this process at 160° F., developed tuberculosis of the 

 spleen as well as local lesions. This led to a repetition of the experiments by this 

 group,5 who reported on December 21, 1926, that three out of twenty-six pigs in four 

 experiments gave similar positives.'' 



It has been suggested that the conflict in results may possibly be due to the fact 

 that the dosage of tubercle bacilli, used to infect the raw milk in the tests by Irwin, 

 Haythorn, and Conover, was considerably greater than in the tests by Prescott and 

 others, and that for this reason a sufficient number of tubercle bacflli remained un- 

 destroyed in the portion injected in the former tests to constitute an infecting dosage 

 to a guinea pig. This emphasizes the desirability of (i) agreement among bacteri- 

 ologists on an approximate standard infecting dosage of tubercle bacilli and other 

 pathogenic organisms for tests on their destruction in mflk, and (2) determining as 

 nearly as possible the minimum infecting dose of the raw mflk, in order that a better 

 comparison of the results of such tests may be made. 



Recent work by Park^ reported in October, 1927, as yet unpublished, indicates that 

 pathogenic strains of hemolytic streptococci are more resistant than tubercle bacilli 

 to destruction by heat. Park reports that hemolytic streptococci commonly found 



' North, C. E., d al.: ibid. p. 98. 



" Beattie, J. M., and Lewis, F. C: Rep. Med. Research Com., Great Britain. 1920. 



3 Prescott, S. C: Am. J. Pub. Health, 17, 221. 1927. 



1 1rwin, R. E., Haythorn, S. R., and Conover, J. R.: Rep. Com. Appointed by Sec. of Health {Pa.) 

 to Study the Eleciropure Process of Milk Treatment. April 13, 1926. 



5 Irwin, R. E., Haythorn, S. R., and Conover, J. R.: ibid. Dec. 21, 1926. 



^Another series of tests was run on this process in June, 1927, by the N.Y. State and City de- 

 partments of health and the U.S. Public Health Service. Results were not available at the time of 

 writing this article. 



'Park, W. H.: "Thermal Death Point of Streptococci," ylw. /. Pub. Health. (In press.) 



