Il8 ESSENTIALS OF BACTERIOLOGY 



nodules containing the characteristic bacilli. In the lungs 

 and the lymphatics similar tubercles are found a general 

 tuberculosis. 



If the animal lingers a few weeks longer, the tubercles 

 becomes necrosed in the center and degeneration occurs, the 

 periphery still containing active bacilli, cavities having formed 

 in the center. 



Since the bacilli die hi course of time, killed by their own 

 products, their number forms no correct guide of the dam- 

 age present: even their absence in the sputum does not pre- 

 clude the absence of a tuberculous process. It is their pres- 

 ence only that warrants a positive declaration. The number of 

 bacilli in a given specimen is no indication of the severity of 

 the disease. 



They are found in the blood only when a vessel has come 

 in direct contact with a tuberculous process through rupture 

 or otherwise. They have been found occasionally hi other 

 secretions milk, urine, etc. 



Man is infected as follows.: 



Through Wounds. Local tuberculosis. 



Through Nutrition. Milk and meat of tuberculous ani- 

 mals. Phthisical patients swallowing their own sputum and 

 causing an intestinal tuberculosis. 



Inhalation. This is the most usual way, probably consti- 

 tuting the cause in nine-tenths of the cases in adults. 



The sputum of phthisical patients expectorated on the 

 floors of dwelling-houses, in handkerchiefs, etc., dries, and 

 the bacilli set free are placed in motion by the wind, or rising 

 with the dust, are thus inhaled by those present. When the 

 sputum is kept from drying by expectoration in vessels con- 

 taining water, this great danger can be avoided. 



Intra-uterine or placental infection has been demonstrated, 

 but is a great rarity. The ovum or human semen is seldom 

 if ever infected, although tubercular infection of the testicle 

 is common. 



Nearly all the cases of supposed heredity can be explained 

 as follows: the young children, possessing very little resist- 



