298 BACTERIA PATHOGENIC TO MAN 



inhabited by healthy persons or the dusts of the streets does so only in 

 an extremely 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 usually free from living bacilli. It is in the coarser though still 

 minute particles, those in which the bacilli are protected by an envelope 

 of mucus, that the germs resist drying for considerable periods. These are 

 carried only short distances by air currents. Such results as those ob- 

 tained by Straus, who on examining the nasal secretions of twenty-nine 

 healthy persons living in a hospital with consumptive patients, found 

 tubercle bacilli in nine of them, must be accepted with some reserve, 

 since we know that in the air there are bacilli which look and stain like 

 tubercle bacilli and yet are totally different. It may be said that the 

 danger of infection from slight contact with tuberculosis is not so great 

 as it is considered by many, but that on this account it is all the more to 

 be feared and guarded against in the immediate neighborhood of con- 

 sumptives. 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, atten- 

 tion may be drawn to the fact that rooms which have been recently 

 occupied by consumptives are not infrequently the means of producing 

 infection (as has been clinically and experimentally demonstrated) 

 from the deposition of tuberculous dust on furniture, walls, floors, etc. 

 Flugge has recently drawn attention to the fact that in coughing, sneez- 

 ing, etc., very fine particles of throat secretion are thrown out and 

 carried by air currents many feet from the patient and remain sus- 

 pended in the air for a considerable time. This is another means of 

 infection, but probably a less frequent one. To encourage us we now 

 have a mass of facts which go to show that when the sputum is care- 

 fully looked after there is very little danger of infecting others except 

 by close personal contact. 



INDIVIDUAL SUSCEPTIBILITY. It is believed by many that in demon- 

 strating the possibility of infection in pulmonary tuberculosis its occur- 

 rence is sufficiently explained; but they leave out another and most 

 important factor in the production of an infectious disease individual 

 susceptibility. That this susceptibility, or "predisposition/' as it is 

 improperly called, may be either inherited or acquired is now an accepted 

 fact in medicine. It is even thought that the physical signs and char- 

 acters the phthisical habit which indicate this susceptibility can be 

 externally recognized. At first the inherited susceptibility was con- 

 sidered more important than the acquired, but now much that was 

 attributed to the former is known to be explained by the fact of living 

 in an infected area. The acquired susceptibility may arise from 

 faulty ^physical development or from depression, sickness, overwork, 

 excessive use of alcohol, etc. Unquestionably, vast differences exist 

 in different individuals in the intensity of the tuberculous process in 

 the lung. That this does not depend chiefly upon a difference in viru- 

 lence of the infection is evident, from the fact that individuals con- 

 tracting tuberculosis from the same source are attacked with different 



