49 



sliglitly bent or even curved. They niay occur singly or in 

 pairs, or even in close-packed masses. They are recognised 

 easily by their size under the microscope, and also by their 

 behaviour with certain staining re-agents. They are not 

 discolourised by a 25% solution of sulphuric acid after 

 staining with fuchsiti. They multiply by fission as well as 

 by spores, are non-motile, and found in greatest numbers just 

 where the disease is spreading. 



Besides being found in the tissues, they are abundant in 

 the sputum of consumptive patients, as well as in the blood 

 and urine. 



They can be cultivated outside the body either on blood 

 serum or glycerine agar — agar jelly at a temperature between 

 95° F. to 105° F. They form little colonies in 10 to 14 days, 

 differing greatly in this resj^ect from the bacillus of diphtheria, 

 which will grow almost in as many hours. 



A high or a low temperature will stop their growth, but the 

 bacillus as well as the spores are very resistant against com- 

 plete destruction. Though a certain amount of moisture is 

 necessary for their growth, they can be dried without losing 

 the power of infection. 



Tubercular matter taken from the lungs of persons buried 

 for years has been found virulent on inoculation. Cold does 

 not seem to kill the bacillus, but growth ceases at a temper- 

 ature of 82° F. 



Heat at 250° F. destroys them, so will a temperature of 

 107*5° F. continued for several weeks. 



The spores retain their virulence under conditions which 

 are inimical to the bacillus, and the chief source of infection 

 is by the spores floating about in the atmosphere. 



What are then the modes of entrance by which the infecting 

 bacillus may gain entrance into the body ? 



(1.) By the respiratory and (2) alimentary tract. (3.) By 

 inoculation. (4.) Another mode of infection — hereditary 

 transmission — will be considered as we go on. The channel 

 of infection often determines the seat of the disease. 



(1.) Aerial Infection through the Respiratory Tract. 

 — In our ordinary surroundings of life the conditions necessary 

 for the multiplication of the bacillus are never present, and 

 we could only have tuberculosis by infection from one 

 individual to another were it not for the fact already men- 

 tioned that the bacilli and their spores retain their vitality 

 and virulence for a long time outside the body. In order 

 that the virus may enter the lungs by the inspired air, the 

 medium on which the micro-organisms develop must dry up 

 and disintegrate into powder or dust. If it be remembered 

 that the sputum of tubercular persons usually furnish the 



