280 BACTERIOLOGY. 
produced tuberculosis in a considerable percentage of 
them; whereas the dust from rooms inhabited by healthy 
persons or the dust of the streets did so only in an ex- 
tremely small percentage. Fliigge is probably right 
in thinking that the dust which is fine enough to 
remain for a long time in suspension in the air is prac- 
tically free from living pathogenic bacteria. It is the 
coarser particles in which the bacilli are protected 
by an envelope of mucus that resist drying for consider- 
able periods. These are carried only short distances 
by air currents. Such results as those obtained by 
Straus, who, examining the nasal secretions of twenty- 
nine healthy persons living in a hospital with con- 
sumptive patients, found tubercle bacilli in nine of 
them, must be accepted with some reserve, since we 
know that in the air there are bacilli derived from 
grasses which look and stain like tubercle bacilli and 
yet are totally different. It has been argued by some, 
from the fact that about one-seventh of all men die from 
tuberculosis, that the tubercle bacilli must be ubiquitous, 
and that precautions are useless; but, as Cornet has 
pointed out, this does not mean that one-seventh of all 
men living, are tuberculous, for no man is tuberculous 
during the entire course of his life, but only for a lim- 
ited period (variously estimated at from three to eight 
years). It may, therefore, be said that the danger of 
infection from tuberculosis in general is not so great 
after all, but that on this account it is all the more to 
be feared and guarded against in the immediate neigh- 
borhood of consumptives. Those who are most liable 
to infection from this source are the families, the nurses, 
the fellow-workmen, and fellow-prisoners of persons 
suffering from the disease. In this connection, also, 
