3 6 ° 
THOMPSON YATES LABORATORIES REPORT 
'As to the question where the inhaled tubercle bacilli come from there is no 
doubt ; certainly they get into the air with the sputum of consumptive patients. By 
coughing, and even speaking, sputum containing bacilli is flung into the air in small 
drops, and can at once infect persons who happen to be near the cougher. But it 
may also be pulverized, when dried, in the linen or on the floor, and get into the air 
in the form of dust.' 
Although it is certain that the sputum expectorated by tubercular individuals is 
most commonly a very dangerous source of infection in the overcrowded and ill- 
ventilated dwellings, workshops, and other rooms occupied by the lower classes ; still, 
there can be but little doubt that infection may arise from the inhalation of dust 
particles in our public thoroughfares and streets, and that this will continue a source 
of public danger until an efficient means of prevention can be inaugurated. 
Brouardel at the same Congress characterized the custom 'of expectorating on 
the ground as a disgusting and dangerous habit,' and stated ' that once the habit has 
disappeared, tuberculosis will decrease rapidly.' 
Tubercle bacilli in sputum expectorated on the street walks are influenced there 
by two physical agencies — desiccation and the action of light — and also are submitted 
to any influence which may be exerted by putrefactive and other organisms in the 
sputum or gaining access to it. It is well known that tubercle bacilli resist the action 
of such organisms for a long period, and in general the expectorated mass has become 
a powdered dust before their action is likely to exert any deleterious effect on the 
tubercle bacilli. 
The action of desiccation has been known for many years. Schill and Fischer 
shewed that tubercle bacilli in sputum, dried in a thin layer, retained their virulence 
for six months ; while Sormani shewed that sputum dried in a thin layer on glass 
was not virulent after four months. Cornet 1 believes that, considering that tubercle 
bacilli may continue virulent in the dust of dried sputum for at least three or four 
months, in the country, where the dust is diluted by a large volume of air, the 
chance of infection thereby is but small ; but in large towns, particularly in the most 
frequented streets in summer or during continued dry weather, the infecting material 
becomes more abundant, and there is danger of infection with the tubercle bacilli 
in street dust. 
Experiments by Nuttall 2 seem to indicate that under favourable temperature 
circumstances tubercle bacilli may multiply in tubercular sputum outside the body. 
There now remains to be considered only the action of light on the tubercle 
bacilli in sputum expectorated on to the street sidewalks. Koch 3 states that ' he was 
able to determine that tubercle bacilli, according to the thickness of the layer in which 
they were exposed to sunlight, were killed in a few minutes to some hours. Also, 
[. Cornet, Zeitsc/i, Hygiene, vol. V, p. 288. 
2. Sternberg, Manual of Bacteriology, p. 381. 
3. Koch, Verhandlungen d. Internatl. Congr., Berlin, 1890, p. 142, 
