486 PATHOGENIC MICROORGANISMS 



two to eight months, varying to some extent with the nature of the 

 culture medium. The viabihty of the bacilU in sputum is of great 

 hygienic importance. In most sputum they may remain aUve and 

 virulent for as long as six weeks, in dried sputum for more than two 

 months."^ 



Five per cent carbolic acid kills the bacilli in a few minutes.^ If used 

 for sputum disinfection, however, where the bacilli are protected by 

 mucus, complete disinfection by this method requires five to six hours. 

 Bichloride of mercury is not very efficient for sputum disinfection be- 

 cause of the formation of albuminate of mercury. 



For room disinfection, formaldehyde gas if thoroughly employed is 

 efficient. Direct sunlight kills tubercle baciUi in a few hours. 



Pathogenicity. — The tubercle bacillus gives rise in man and suscep- 

 tible animals to specific phenomena of inflarnmation which are so 

 characteristic that a diagnosis of tuberculosis may usually be made on 

 the basis of the histological examination of material, even without the 

 finding of tubercle bacilli. The foci of inflammation known as tubercles 

 have been systematically studied by Baumgarten ^ and many others 

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

 anatomy. 



In man, tuberculosis is by far the most common of diseases. 

 Naegeli,^ in -a large series of autopsies, found lesions of healed or active 

 tuberculosis in an appalUng percentage of cases. His figures are in- 

 teresting in showing not only the frequency of the disease, but its rela- 

 tion 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 when occurring. From the 

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

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

 cases. Between the ages of 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 in number, healed lesions increased. 



In 1900, at a public hearing of the New York Tenement House 

 Commission, Pryor ^ stated that the average yearly mortality from 



1 Schell und Fischer, Mitt. a. d. kais. Gesundheitsamt, 1884. 



2 De Toma, Ann. di med., 1886. 

 ^Baumgarten, Berl. klin. Woch., 1901. 



' Naegeli, Virchow's Arch., cix, 1900, p. 462. 

 ' Pryor, Med. News, Ixxvii, 1900. 



