CHAPTER XXL 



THE BACILLUS OF TUBERCULOSIS. 



A KNOWLEDGE of phthisis was certainly present among men at the 

 time from which our earliest medical descriptions come. For over 

 two thousand years many of the clearest-thinking physicians have 

 considered it a communicable disease; but it is only within compara- 

 tively recent times that the infectiousness of tuberculosis has become 

 an established fact in scientific medicine. Villemin, in 1865, by infecting 

 a series of animals through inoculations with tuberculous tissue, showed 

 that tuberculosis might be induced, and that such tissue carried the 

 exciting agent of the disease. Baumgarten demonstrated, early in 1882, 

 bacilli in tissue sections which are now known to have been the tubercle 

 bacilli. But these investigations and those of others at the same time, 

 though paving the way to a better knowledge of the disease, proved to 

 be unsatisfactory and incomplete. The announcement of the discovery 

 of the tubercle bacillus was made by Koch in March, 1882. Along 

 with the announcement satisfactory experimental evidence was pre- 

 sented as to its etiological relation to tuberculosis in man and in sus- 

 ceptible animals, and its principal biological characters were given. 

 An innumerable number of investigators now followed Koch into this 

 field, but their observations served only to confirm his discovery. 



Distribution of Bacilli. They are found in the sputum of persons 

 and animals suffering from pulmonary or laryngeal tuberculosis, either 

 free or in the interior of pus cells; in miliary tubercles and fresh caseous 

 masses in the lungs and elsewhere; in recent tuberculous cavities in the 

 lungs; in tuberculous glands, joints, bones, mucous membranes, and 

 skin affections. 



Morphology. The tubercle bacilli are slender, non-motile rods of 

 about 0.3/* in diameter by 1.5 to 4//. in length. (Plate I., Figs. 1, 2, 

 and 3.) Commonly they occur singly or in pairs, and are then usually 

 slightly curved; frequently they are observed in smaller or larger bunches. 

 Under exceptional conditions branching and club-shaped forms are 

 observed. Injected into the brain, kidney, and other tissues in rabbits 

 a growth frequently occurs in which forms similar to actinomyces 

 develop. The tubercle bacillus clearly belongs among the higher forms 

 of bacteria and is closely allied to actinomycosis. The same is true for 

 some of the timothy and other acid-fast bacilli. In stained preparations 

 there are often seen unstained portions. From two to six of these 

 vacuoles may sometimes be noticed in a single rod. In old cultures 

 irregular forms may develop, the rods being occasionally swollen at 

 one end or presenting lateral projections. Here also spherical granules 



