PASTEURIZATION 205 
also sometimes transmitted by milk, has not been iden- 
tified. Of the organisms mentioned, the tubercle bacillus 
is the most resistant to heat, with the possible exception 
of some varieties of streptococci. The streptococci of 
septic sore throat are destroyed by heating at 140° F. 
(60° C.) for 30 minutes (Davis) or at 145° F. (62.8° 
C.) for 20 minutes (Hamburger), and exposure to a 
temperature of 125.6 to 143.6° F. (52 to 62° C.) for 
30 minutes is sufficient to kill Streptococcus pyogenes 
(Hitchens). There are some varieties of streptococci 
which are more resistant to heat, but we have no reason 
to believe that those which occur in milk are pathogenic. 
It seems very probable that heating milk sufficiently to 
destroy tubercle bacilli will also kill any pathogenic strep- 
tococci which may be present. A temperature of 140° F. 
(60° C.) for 2 minutes will destroy the bacilli of typhoid 
fever and diphtheria. The question of the amount of 
heat required to destroy the pathogenic organisms which 
occur most frequently in milk consequently resolves it- 
self into a question of how much heat is necessary to kill 
the tubercle bacillus. The evidence on this point must 
therefore be considered. 
Bang found that heating milk momentarily at 185° 
F. (85° C.) destroyed tubercle bacilli in naturally in- 
fected milk, and Jensen reports experiments in which 
tubercle bacilli in milk were killed by a few moments 
exposure to 158 to 176° F. (70 to 80° C.). On the other 
hand, Grimmer and other investigators are of the opinion 
that, when the exposure is momentary, a temperature of 
at least 194° F. (90° C.) is necessary to insure the de- 
struction of the bacilli in all cases. 
Concerning the effects of a more prolonged exposure 
at lower temperatures, experimental results are even 
