40 
He limited his investigation to the effects of 60° upon artificially 
infected milk and demonstrated by a series of experiments, which 
should be consulted in the original to appreciate their full force and 
value, that an exposure to 60° for fifteen minutes is enough to kill 
tubercle bacilli suspended in distilled water, normal salt solution, 
bouillon and milk, provided that in the case of milk the production 
of a surface pellicle is prevented. The pellicle which forms during 
the exposure may contain living tubercle bacilli after sixty minutes 
exposure at 60° C. 
Smith concluded that (1) tubercle bacilli when suspended in dis- 
tilled water, normal salt solution, bouillon and milk are destroyed at 
60° C. in fifteen to twenty minutes (the larger number are destroyed 
in five to fifteen minutes); (2) when tubercle bacilli are suspended 
in milk the pellicle which forms during the exposure at 60° C. may 
contain liHng bacilli after sixty minutes. He also states that these 
experiments demonstrate that tubercle bacilli are no more resistant, 
to heat than many other bacilli not producing spores. 
Forster and De Man, had they used a homogeneous suspension in 
normal milk, must have arrived at similar results with their sealed 
tubes, where a pellicle does not form; but as Barthel and Stenstrom 
have shown, the pathological material from tuberculous udders, prob- 
ably because of its abnormal reaction, is especially prone upon heat- 
ing to the formation of little clumps of proteid coagula, which exert 
a protective influence against heat upon the tubercle bacilli. 
Morgenroth,® 1900, apparently had not the benefit of Smith’s work 
when he did his own experiments. He determined that 70° for ten 
minutes or 100° momentaril}^ did not kill the tubercle bacilli in milk 
from tuberculous udders. Scum formation was not mentioned and 
the minutiae of the experiments are omitted. He worked with the 
^Hhermophore,” an apparatus which maintains a heat of 55° or more 
for several hours, and says that artificially inoculated milk is freed 
from living tubercle bacilli in this apparatus after three hours, two 
hours being insufficient. 
Kobrak,^ 1900, states that the thermophore kills tubercle bacilli 
in milk infected with sputum in four, but not in three, hours. The 
temperature ranged probably somewhat over 50° during this time. 
Beck,^' 1900, concludes from his experiments that raising milk to 
the boiling point is insufficient to kill the contained tubercle bacilli, 
but that they are surely killed by three minutes boiling. He also 
«Morgenroth; Versuche iiber Abtodtung von Tuberkelbacillen in Milch. Hyg. 
Runds., vol. 10, 1900, p. 685. 
&Kobrak: Die Bedeutung des Milch-Thermophores fiir die Sauglingsernahrung. 
Zeit. f. Hyg., 1900, vol. 34, p. 518. 
c Beck: Experimentelle Beitrage zur Untersuchungen iiber die Marktmilch. Dent. 
Viertelj. f. off. Gesundhpfl., vol. 32, 1900; p. 430. 
