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, 



