548 
The vitality and virulence of tubercle bacilli in dairy products is 
ver} r different from their rapid destruction in sputum, and we must 
also bear in mind that they are not on the floor, or in the air, or in 
other places from which they may or may not gain access to our 
bodies, but that they are contained within articles of food with which 
they will certainly be introduced into our bodies. 
Broers,® whose work on tuberculous dairy products is based on 
careful observations, found that tubercle bacilli will live three days in 
milk, even when it has undergone changes to make it unfit for use as 
food, twelve days in buttermilk, and that they certainly remain 
virulent in butter three weeks. As milk and buttermilk are rarely 
used in a raw state after they are more than three days old, it is not 
necessary to show that the tubercle bacilli they may contain will re- 
main alive and virulent longer than Broers has recorded. The length 
of time the bacilli remain virulent in butter is another matter, and 
regarding it the available data are very contradictory, as is shown by 
Cornet, * 6 who says: 
Laser could find no live tubercle bacilli in butter after twelve days ; Heim 
records that all tubercle bacilli eventually die in butter, and that their maximum 
life in it is thirty days ; Gasperini found a reduction of virulence after thirty 
days, though the bacilli were still alive after one hundred and twenty days ; and 
Dawson did not observe a reduction of virulence until after three months, and 
claims to have produced tuberculosis in a guinea pig by inoculating it with 
butter eight months old. 
As the two extremes, twelve days and eight months, are too far 
apart to be satisfactory, an investigation relative to this matter 
was undertaken at the experiment station of the Bureau of Animal 
Industry. 0 
Butter was made from the milk of a cow affected with udder 
tuberculosis, and tested from time to time by making guinea-pig 
inoculations with it. The butter was salted at the rate of 1 ounce of 
salt to the pound of butter, and the conclusions drawn regarding it 
are as follows : 
The guinea-pig inoculations show that tubercle bacilli in ordinary salted 
butter undergo no attenuation in forty-nine days; that they are still highly 
virulent after ninety-nine days, or more than three months, and that they are 
still alive after one hundred and thirty-three days. 
Since these tests were made it was found that the bacilli are still 
alive after one hundred and sixty days, which indicates that Daw- 
son’s period of eight months is not an exaggeration. 
As the investigations of the experiment station regarding the long- 
retained virulence of tubercle bacilli in butter called out a popular 
a Zeitschrift fiir Tuberkulose, Vol. X, No. 3. 
6 Die Tuberkulose, Vienna, 1907, p. 124. 
c Bureau of Animal Industry Circular No. 127. 
