332 TUBERCULOSIS AS A TYPE OF BACTERIAL DISEASE 



which the tubercle bacillus gains access to the human body are three, 

 namely, through the skin, and through the alimentary and respiratory 

 systems. A great variety of cases of skin infection are on record, 

 although the uninjured epidermis affords a fairly reliable protection, so 

 that simple contact with tuberculosis sputum does not suffice to pro- 

 duce infection if the skin be uninjured. The exact means and occasion 

 of entry are innumerable. Wounds play a great part in rendering 

 possible the invasion by tubercle bacilli. Infection by the alimentary 

 tract takes place in a variety of ways. The bacilli may be carried 

 in with air in mouth-inspiration, by dirty objects placed in the mouth 

 (in children), by kissing tuberculous persons, or by the ingestion of 

 infected food. Thus, we may have tuberculosis of the mouth and 

 tonsils, of the stomach, and pf the intestine and other abdominal 

 organs, including the mesenteric glands. Elsewhere we remark upon 

 the comparative rarity of primary abdominal tuberculosis in man, 

 though the disease is more common in animals. 



The chief channel of infection is, of course, the respiratory tract, 

 and the two means by which tubercle bacilli thus reach the body 

 are (a) inhalation of the dust of dried tuberculous sputum, and 

 (b) the inhalation of moist particles from the cough-spray of a 

 phthisical patient. "Wherever tuberculous sputum is allowed to dry 

 the risks are great that the dust so produced may be inhaled in a 

 virulent form, and lodging at one or more points may set up varying 

 degrees of tuberculosis. This broad fact is based upon experimental 

 and clinical evidence. Tuberculosis has been produced experimentally 

 in animals in this way, and there is clinically the overwhelming- 

 frequency of tuberculosis of the lungs among men exposed to just 

 such a manner of infection. But Koch, Fliigge, and others have 

 shown that not only is sputum a source of infection when dried 

 and pulverised, but also when disseminated by coughing, shouting, 

 etc., in the form of minute moist particles of spray. Koch exposed 

 rabbits, guinea-pigs, rats, and mice to an infected spray for half an hour 

 on three successive days, and produced tuberculosis in every animal. 

 Heymann found that such spray particles from human beings 

 inoculated into guinea-pigs produced tuberculosis. Most of the 

 droplets are large and settle rapidly, but some may remain suspended 

 in the air for more than an hour, retaining, of course, their virulent 

 properties. Heymann found the duration of life of the bacilli in these 

 droplets was eighteen days in the dark, and three days when exposed 

 to light. Under ordinary circumstances and an absence of draughts, 

 the zone of danger from a coughing consumptive extends to a 

 distance of about three feet. It must be remembered that the 

 tubercle bacilli in the moist particles of cough-spray, are probably of 

 higher virulence than those in dried sputum dust, and therefore it 

 seems reasonable to suppose that the cough-spray is the most 



