39 
case of experiments conducted with milk artificially contaminated 
with pieces of tubercular tissue, by the fact that clumps of consid- 
erable size (too large to pass through the inoculating needle and 
requiring glass pipettes for inoculation) were added to the milk, and 
that these would in some manner protect the bacilli; and in the case 
of naturally tuberculous milk by the probability of protection by 
coagula — especially prone to occur in the concentrated pathological 
product — and by the pellicle which forms on the surface of heated 
milk. 
Considering the inoculation experiments with both the natural and 
the artificial tuberculous milk, the following minimum lethal tempera- 
ture exposures are found in the tables: 50° C. killed surely only after 
fifteen hours ; 55°, after seven hours; 60°, after eight hours; 65°, after 
four hours;® 70°, after forty-five minutes; 75°, after thirty minutes; 
80°, — ; 85°, after two and one-half minutes; 90° did not kill. 
This summary shows how Woodhead’s results contradict them- 
selves and differ from those of other observers. When the results 
with the naturally tuberculous milk alone, are considered, the results 
accord more with Bang’s; for example: 60° kills surely after forty- 
five minutes; 65°, after two and one-half minutes; 70°, after two 
and one-half minutes. 
Marshal,^ 1899, first sterilized milk, then added tuberculous mate- 
rial from cows, injected control animals vdth this suspension, and 
then exposed the milk in shallow dishes in a ‘^pail sterilizer” placed 
on a water bath. Heat was applied to the water bath until the tem- 
perature in all parts of the vapor chamber was 68°. This tempera- 
ture was maintained twenty minutes. The shallow layer of milk 
was devised to secure equal temperature throughout the milk. The 
controls died in a few weeks of tuberculosis, but none of the test animals 
killed and examined at the same time showed any signs of tubercu- 
losis. He states that from other experience he knows that 60° for 
ten minutes will not kill tubercle bacilli, but does not detail the experi- 
ments upon which this conclusion is based. 
Theobald Smith,'" 1899, contributed an article to the literature of 
this subject which marks an era in the history of the pasteurization 
of milk based upon the thermal death point of the tubercle bacillus. 
Smith’s experiments were most carefully performed. Many pitfalls 
and errors which some of his predecessors had fallen into were avoided 
and pointed out. The only possible objection to the work, which 
applies with equal force to all laboratory experiments, is that it was 
not done on a scale of practical dairy pasteurization. 
« No experiment between three and four hours; killed after two hours. 
& Marshal, Charles E.; Killing the tubercle bacillus in milk. Michigan State 
Agricultural College experiment station, Bull. 173, 18997 
c Smith, Th. : The thermal death point of tubercle bacilli in milk and some other 
fluids. Journ. Exper. Med., vol. 4, 1899, p. 219. 
