36 
bles the virus that he believes it is no longer able to infect when fed 
by way of the digestive tract. Ten years later Bang was obliged to 
correct in part some' of his early results. 
Man}^ observers nowadays would regard these results as indicating 
an undul}^ high resistance of the organism and would suspect that 
Bang gave the tubercle bacillus a handicap in three ways: (1) In 
using pathological milk prone to form little clots on heating, which 
protect the tubercle bacilli (see Barthel and Stenstrom); (2) in not 
avoiding the formation of the protective surface pellicle (see Th. 
Smith, Russell and Hastings, Hesse), and (3) possibly in failing to 
differentiate the lesions caused by dead tubercle from those caused by 
living germs (Smith, Miller, Prudden, and Hodenphyl). 
Bonjioff,® 1892, did not work with milk, but gives some data 
obtained with pure cultures of tubercle bacilli in liquid media, vdiich 
ma}^ be accepted as contributor}^ evidence. Young cultures, the 
ultimate antecedents of which are not stated, were exposed in test 
tubes placed in a water-bath, the temperature being observed on a 
thermometer placed inside the tube. Guinea pigs were inoculated 
intraperitoneally before and after exposure. The significant findings 
are, that while 50° for sixty minutes failed to kill the bacteria, 60° for 
twenty minutes did kill them. Exposures of less than twenty 
minutes were not made. The author unfortunately had some diffi- 
culty in preventing the development of lung tuberculosis in his 
animals. For instance, the pigs receiving the material heated to 60° 
for forty minutes, 70° for sixty minutes, and 80° momentarily, 
developed what he calls and is at considerable pains to differentiate as 
inhalation tuberculosis. 
Grancher and Ledoux-Lebard,^ 1892, appreciated the occurrence of 
lesions produced by dead tubercle bacilli in their inoculated animals. 
They showed that human tubercle bacilli are more sensitive to the 
action of temperatures of 50° C. than are avian tubercle bacilli. 
Heating the avian bacilli to 50° or 60° for fifteen minutes did not kill 
them. Animals inoculated died of tuberculosis. However, the 
organisms heated to 60° were attenuated. Heating to 70° under the 
same conditions noted was sufficient to destroy the power of the 
avian tubercle bacilli to infect laboratory animals. 
They heated cultures of human tubercle bacilli suspended in dis- 
tilled water and found that five minutes at 60° sufficed to attenuate 
the virulence. Heating to 60° for ten minutes and twenty minutes 
also greatly attenuated the virulence. When heated to 70° C. for 
one, two, five, or ten minutes the tubercle bacilli were killed. 
aBonhoff ; Die Einwirkung hoherer Warmegrade auf Tuberkelbacillen-Reinkul- 
turen. Hyg. Runds., vol. 2, 1892, p. 1009. 
& Grancher, J., and Ledoiix-Lebard; Tuberculose aviaire et humaine. Arch, de 
med. exper. et d’anat. pathoL, vol. 4, 1892, p. 1. 
