MANNER OF INFECTION. 193 



the respiratory tract. The bacillus is inhaled with the im- 

 palpable dust in which it is contained. It was formerly 

 believed that all dust contained the bacillus, but this has 

 been disproved by more recent investigations, which show 

 that it is found only in the dust of places frequented by con- 

 sumptives. It is also possible, although unusual, to inhale 

 the germ directly from a patient when he sneezes or coughs. 

 The mucus which is expelled with the effort may contain the 

 bacillus. For this reason the physician should never stand 

 in front of a patient when he is conducting an examination 

 of the throat or chest. Patients should be urged to cover the 

 face with a cloth or handkerchief when they cough or sneeze. 

 Nuttall says that from one-half to three billion virulent 

 tubercle bacilli are expectorated by a tubercular patient in 

 the course of twenty-four hours. The necessity of extreme 

 precautions to prevent infection, especially of the medical 

 attendant and the patient's family, is very evident. 



Persons susceptible to tuberculosis should be exceedingly 

 careful not to increase the liability of infection by living with 

 a tubercular patient or consorting with him longer than 

 is absolutely necessary. The patient should do all in his 

 power to prevent his becoming a nidus of infection for others. 

 Bacilli contained within a small particle of mucus remain 

 alive for a long time, and the danger of infection is much 

 greater from this source than from the bacilli contained in 

 dust which has been exposed to light, and especially sunlight, 

 for some time. 



Personal susceptibility is a very essential factor in the con- 

 traction of the disease. It is possible for a perfectly healthy 

 individual to inhale the tubercle bacillus without acquiring 

 the disease. His active phagocytes will dispose of the germ. 

 At autopsies the bronchial and mediastinal lymph-glands fre- 

 quently present evidences of tubercular invasion, although 

 the patients may not have exhibited any symptoms of tuber- 

 culosis during their lifetime. This is an evidence of phago- 

 cytosis ; or of infection with a bacillus which was considerably 

 attenuated. It has been said that 80 per cent, of all persons 

 post-mortemed show evidences of tubercular infection, and 

 yet only (!) one-seventh of the population die from tubercu- 



13 Bact. 



