THE THERMAL DEATH POINTS OF PATHO- 
GENIC MICRO-ORGANISMS IN MILK.® 
By Milton J. Rosenau, 
Surgeon and Director Hygienic Laboratory, U. S. Public Health and Marine- Hospital 
Service. 
INTRODUCTION. 
The temperature at which milk should be pasteurized hinges on the 
thermal death points of the pathogenic micro-organisms wliich con- 
taminate it. The pathogenic micro-organisms most frequently found 
in market milk are those causing tuberculosis, t}^phoid fever, diph- 
theria, scarlet fever, dysentery, and Malta fever. Fortunately none 
of the organisms causing the above-mentioned diseases has resisting 
spores. Moderate degrees of heat are, therefore, sufficient to render 
milk safe so far as these dangers are concerned. The streptococci, 
staphylococci, and most of the bacteria associated with infantile 
diarrhea are also readily destroyed by heat. 
Although it would appear to be a comparatively simple matter to 
determine precisely the temperature at which micro-organisms die, 
such work is in fact surrounded by many difficulties and pitfalls; 
different investigators have come to widely different results. Some 
of these discrepancies are only apparent and may be explained by the 
relation of time to temperature. The longer the time of exposure, the 
lower the temperature necessary to kill any organism. Differences 
in methods are also responsible for differences in results. Thus some 
workers start with the fluid containing the micro-organisms to be 
tested at room temperature and raise it to the desired temperature; 
others introduce the bacteria after the fluid has been heated. 
I 
Care must be taken in thermal death-point work to see that the 
entire volume of the water bath, as well as the fluid medium tested, has 
approximately the same temperature throughout. Unless attention 
to this point is given, a difference of 5° to 10° C. between the top 
^Manuscript submitted for publication February 11, 1908. 
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