THE TUBERCLE BACILI ! 487 



and descriptions may be found in any text-book of pathological 

 anatomy. 



In man, tuberculosis is the most common of diseases. Naegeli's sta- 

 tistics, based on a large series of autopsies, show not only the frequency 

 of thc> disease, but its relation to age. Before one year of age, he finds it 

 very rare. From the first to the fifth year it is rare, but usually fatal. 

 From the fifth to the fourteenth year, one-third of his cases showed 

 tuberculosis; from the fourteenth to the eighteenth year, one-half of 

 the cases. Between eighteen and thirty, almost all the cases examined 

 showed some trace of tuberculous infection. Three-quarters of these 

 were active, one-quarter healed. Two-fifths of all deaths occurring at 

 these ages were due to tuberculosis. After the age of thirty, active 

 lesions gradually diminished, healed lesions increased. 



In 1900 Pryor l stated that the average yearly mortality from 

 tuberculosis in Xew York amounted to 6,000, and that in Manhattan 

 alone there were constantly 20,000 tuberculous persons. Cornet 2 esti- 

 mates that in 1894 the deaths in Germany from all other infectious 

 diseases amounted to 116,705, those from tuberculosis alone to 123,904. 

 Similar statistics might be chosen from the health reports of any large 

 city. White the disease is less common in rural districts than in large 

 towns, the difference is not so striking as is generally supposed. 



In man, pulmonary infection is the commonest type. Besides this, 

 tuberculous processes may be found in the skin, the bones, the joints, 

 the organs of special sense, and the abdominal viscera and peritoneum. 

 No part of the human body is exempt from the danger of infection. 



Infection in man may take place by inhalation, through the skin 

 or the digestive apparatus. V. Behring 3 has expressed the belief that 

 a large percentage of all cases of tuberculosis originate in childhood 

 from infection through the intestinal tract. He determined that 

 tubercle bacilli may penetrate the intestinal mucosa without causing 

 lesions. Behring's contention has caused a great deal of discussion, 

 and the question he has raised is intimately bound up with the problem 

 of the virulence of bovine tubercle bacilli for human beings, as he as- 

 sumes that the infection is due to the use of infected milk. 



The problem is plainly of the greatest importance, and for this 

 reason has been diligently investigated during the last few years. The 

 only reliable method of approaching it has been to isolate the tubercle 



1 Pryor, Med. News, Ixxvii, 1900. 



1 Cornet, "Die Tuberculose," Wien, 1899, p. 1. 



* v. Behring, Deut. med. Woch., 39, 1903. 



