THE TUBERCLE BACILLUS 597 



cases it does not seem likely that they are so distributed in anything like 

 the high percentages found by Rosenberger. 31 



Although, therefore, in patients suffering from tuberculosis, the 

 presence of the tubercle bacilli in the blood is generally slight or intermit- 

 tent, there may be times when large numbers of tubercle bacilli are 

 thrown into the blood stream, and, according to the manner and quan- 

 tity thus distributed, secondary foci or general miliary tuberculosis may 

 occur. 



Bacillus tuberculosis (typus humanus) is pathogenic for guinea- 

 pigs, less markedly for rabbits, and still less so for dogs. It is slightly 

 pathogenic for cattle, a question spoken of more extensively below. 



Secondary Infection in Tuberculosis. An important consideration 

 in the symptomatology and prognosis of pulmonary tuberculosis is the 

 fact that on the basis of the chronic inflammatory condition of bronchii 

 and alveoli in the neighborhood of tuberculous processes in the bron- 

 chiectatic cavities and perhaps in cavities communicated with bron- 

 chioles, masses of bacteria of various species may accumulate and habit- 

 ually lodge. Staphylococci, streptococci, Gram-negative cocci, and 

 frequently influenza bacilli may be present in such cases and materially 

 contribute to the illness of the patient by superimposing acute and 

 subacute inflammatory processes upon the tuberculous one. 



FREQUENCY AND TRANSMISSION 



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

 statistics, based on a large series of autopsies, show not only the fre- 

 quency of the 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 occur- 

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

 active lesions gradually diminished, healed lesions increased. 



In 1900 it was stated that the average yearly mortality from tuber- 

 culosis in New York amounted to 6000, and that in Manhattan alone 

 there were .constantly 20,000 tuberculous persons. Cornet estimates 



31 Suzuki and TaJcaki, Centralbl. f. Bakt., Ixi, 1911. 



