BACILLUS OF TUBERCULOSIS. 287 
length of time during which the tubercle bacillus re- 
tains its virulence, and whether there are any naturally 
attenuated varieties. According to experimental in- 
vestigations, the virulence of dried tubercular sputum 
is not suddenly but gradually lost, a certain pro- 
portion of it retaining its specific infective power 
under ordinary conditions, as in a dwelling-room, for 
at least two or three months. An instance is reported 
by Ducor (Paris, 1890) of a healthy family having 
been infected with tuberculosis from living in a room 
which had been occupied by a consumptive two years 
before, and on examining the sputum-stained wall-paper 
not only were tubercle bacilli found in it, but upon being 
inoculated into guinea-pigs they died of tuberculosis. 
Attenuation. Metschnikoff states that when kept 
at a temperature of 42° C. for some time the tubercle 
bacillus undergoes a notable diminution in its patho- 
genic power, and that when kept at a temperature of 
43° to 44° C. it after a time only induces a local abscess 
when injected subcutaneously into guinea-pigs. The 
experiments of Lote also indicate that an attenuation 
of virulence has occurred in the cultures preserved in 
Koch’s laboratory, originating in 1882 from the lungs 
of a tuberculous ape. A culture of ours which we ob- 
tained from Trudeau, and which has grown now either 
at Saranac or in our laboratory for six years, is no 
longer capable of causing tuberculosis in guinea-pigs, 
although originally virulent. 
Mixed Infection. Some time ago attention was drawn 
to the fact that tuberculosis, whether of the lungs, 
lymphatics, or cold abscesses, was often a mixed in- 
fection. The other micro-organisms with which the 
tubercle bacillus is most commonly associated are the 
