Feb. 15, 191S Colon Bacilli and Pasteurization 409 



(2) There is a marked difference in the effect of heating at 60° C. 

 (140° F.) and at 62.8° C. (145° F.). Although there is only a difference 

 of 2.8° C.,or 5° F., 87.3 per cent of the cultures which survived at 60° C. 

 (140° F.) were destroyed at 62.8° C. (145° F.). 



(3) Considerable variation was found in the thermal death point of 

 the colon bacilli which survived 62.8° C. (145° F.). When the 12 cul- 

 tures which survived were heated again at the same temperature, it was 

 found that many did not survive and in each repeated heating different 

 results were obtained. 



It seems evident that 62.8° C. (145° F.) maintained for 30 minutes is a 

 critical temperature for colon bacilli. 



(4) Among the 174 cultures studied all were found to have a low 

 majority thermal death point, but were able to sur\'ive pasteurizing tem- 

 peratures on account of the survival of a few cells. 



(5) The colon test as an index of the efficiency of the process of pas- 

 teurization is complicated by the ability of certain strains to survive a 

 temperature of 62.8° C. (145° F.) for 30 minutes and to develop rapidly 

 when the pasteurized milk is held under temperature conditions which 

 might be met during storage and delivery. 



The presence of a large number of colon bacilli immediately after the 

 heating process may indicate improper treatment of the milk. 



(6) If milk is pasteurized at a temperature of 65.6° C. (150° F.) or 

 above for 30 minutes, we should not expect, from our results, that any 

 colon bacilli would survive. Consequently under such conditions the 

 colon test for the efficiency of pasteurization may be of value. It must 

 be remembered, however, that a study of more cultures may reveal 

 strains of colon bacilli that are able to sur\'ive this and even higher tem- 

 peratures. 



LITERATURE CITED 



(i) Avers, S. H., and Johnson, W. T., Jr. 



1913. A study of the bacteria which survive pasteurization. U. S. Dept. Agr. 



Bur. Aniin. Indus. Bui. i6i, 66 p., 3° fig. 

 (2) 



1914. Ability of streptococci to survive pastetuization. In Jour. Agr. Research, 



V. 2, no. 4, p. 321-330, 3 fig. 



(3) Gage, S. de M., and Stoughton, Grace van E. 



1906. A study of the laws governing the resistance of Bacillus coli to heat, fn 

 Technol. Qiuu't., v. 19, no. i, p. 41-54. 



(4) Geuns, Jb. van. 



i88g. Uebcr das " Pasteurisiren " von Bacterien. Ein Beitrag ztir Biologic der 

 Mikroorganismcn. In Arch. Hyg., Bd. 9, p. 369-402. 



(5) Jong, D. A. de, and Graaff, W. C. de. 



1906. Die Coli-KontroUc der pasteurisierten Milch. Jn Ncdcrland. Weekbl. 

 Zuivclber. Veeteelt, deel 12, afd. 37-38. Abstract in Milch w. Zcntralbl., 

 Jahrg. 3, Heft 6, p. 265-268. 1907. Original not seen. 



