30 
According to the work of Kitasato most of the tubercle bacilli in 
sputum, in cavities, and even in the tissues, are dead. This opinion 
was based largely upon negative results obtained by cultural meth- 
ods. As our present cultural methods do not give trustworthy evi- 
dence upon the viability of the tubercle bacillus, further work upon 
the subject is necessary, especially as Straus confirmed the inade- 
quacies of such methods, particularly in obtaining first cultures of 
tubercle bacilli. A certain acclimatization is necessary for their 
ready growth upon artificial media. It is true that Kitasato claims 
to have seen, in some cases, inoculation into guinea pigs fail, but 
Straus and Park have made analogous experiments with opposite 
results. 
THE SHORT LIFE OF CULTURES CONTRASTED WITH THE LONG LIFE 
UNDER UNFAVORABLE CONDITIONS. 
The comparatively short life of pure cultures of the tubercle bacillus 
under most favorable conditions contrasts strangely with the long 
life claimed for the organism under unfavorable conditions. It ap- 
pears that the life of the tubercle bacillus in cultures is shorter the 
more rapid and more luxuriant the growth. 
Cornet states that serum cultures remain alive about six months; 
glycerin-agar cultures are often partially or wholly dead in six to 
eight weeks. It appears that cultures of avian tubercle retain their 
vegetability and pathogenic power much longer : according to Maffucci, 
even two years. Straus states that cultures of human tubercle are 
only exceptionally capable of reproduction after five to six months; 
after eight to twelve months they fail regularly. The virulence of the 
cultures likewise diminishes with age. According to Theobald Smith, 
tubercle cultures are usually dead after three months. 
THE THERMAL DEATH POINT. 
In a recent publication 0 I reported the results of my experiments 
upon the thermal death points of pathogenic micro-organisms in milk. 
Nine experiments were made with five different cultures of the bovine 
tubercle bacillus. The conclusion was drawn that the tubercle bacil- 
lus in milk loses its infective properties for guinea pigs when heated to 
60° C. and maintained at that temperature for twenty minutes, or 
to 65° C. for a much shorter time. 
It should be remembered that the milk in these tests was very 
heavily infected with virulent cultures, as indicated by the prompt 
death of the control animals. Milk would practically never contain 
such an enormous amount of infection under natural conditions. It 
a Hyg. Lab. Bull. No. 42 , U. S. Public Health and Marine-Hospital Service. A 
complete review of the literature upon the subject will be found upon pp. 34-47 of the 
above publication. 
