THE MILK CONTRACTOR 277 



Ability of the Streptococci to Survive Pasteurization. Because the 

 Smith Streptococcus often is conveyed from man to the udder of the 

 cow and causes milk-borne outbreaks of septic sore throat and because 

 garget, a common affection of the cow's udder, is often caused by strepto- 

 cocci, the ability of streptococci to withstand pasteurization excited inter- 

 est. The question was investigated by Ayres and Johnson. They found 

 that the thermal death point of 139 cultures of streptococci isolated from 

 cow's feces, from the udder, from the mouth of the cow and from milk and 

 cream showed a wide variation when the organisms were treated for 30 

 min. under pasteurizing conditions. 



At 140F., the lowest pasteurizing temperature, 89 cultures, or 64.03 

 per cent., survived; at 145F., the usual pasteurizing temperature, 46 

 cultures, or 33.07 per cent. ; at 160F., 2.58 per cent. ; and at 165F. all were 

 killed. 



On the whole, streptococci from the udder were less resistant and those 

 from the milk and cream were more so than those from the mouth of the 

 cow and from cow's feces. 



At 140F. all of the 18 cultures from the milk and cream survived; at 

 145F. 17, or 94.94 per cent., and at 155F., nine cultures, or 50 per cent., 

 withstood the heating; all of the cultures died on exposure to 165F. for 

 20 min. 



Among the 139 cultures of streptococci there were 22 that formed long 

 chains and that were considered typical streptococci; the rest were held 

 to be atypical. Of the typical streptococci 12, or 54.54 per cent., survived 

 heating at 135F. for 30 min., 9, or 40.91 per cent., survived at 140F., 

 and a single culture, or 4.54 per cent., withstood heating at 145F. At 

 150F. for 30 min. all of the typical streptococci were destroyed.' 



The 117 atypical streptococci were more resistant. At 140F., 

 68.37 per cent, survived; at 145F., 38.46 per cent.; at 160F., 2.56 per 

 cent. ; while at 165F. all were destroyed. 



The authors conclude that two classes of streptococci survive pas- 

 teurization, viz. : (1) Streptococci that have a low majority thermal death 

 point but among which a few cells are able to survive the pasteurizing 

 temperature. This ability of a few streptococci to survive the pasteur- 

 izing temperature may be due either to certain resisting characteristics 

 peculiar to a few cells or to some protective influence of the milk. (2) 

 Streptococci having a high majority thermal death point. These survive 

 because the majority thermal death point is above the pasteurizing tem- 

 perature. This ability to withstand heating is a permanent character- 

 istic of certain strains of streptococci. These experiments are comparable 

 to commercial pasteurization by the holder process but had more cultures 

 been examined other results possibly might have been obtained. 



Effect of Pasteurization on Mould Spores. The effect of pasteuriza- 

 tion on mould spores has recently been studied by Thorn and Ayres. The 



