126 TUBERCULOSIS. 



CHAPTER XI. 



TUBERCULOSIS. 

 Bacillus Tuberculosis. 



History. That tuberculosis, the scourge of the human 

 race, was caused by a microorganism, had long been sus- 

 pected there is no doubt, but it was not until Koch's dis- 

 covery of the bacillus tuberculosis in 1882 that this was at 

 all proved. (Plate II.) 



Morphology. The Bacillus tuberculosis is a strict parasite. 

 It is aerobic and grows at the temperature of the human 

 body. It is a slender rod from 1.5 to 3.5 mikrons in length, 

 and from 0.2 to 0.5 mikron in breadth, occurring singly or in 

 pairs united by their narrow extremities. 



It is found in all tuberculous growths and secretions, but 

 especially in the sputum of tuberculous patients, where its 

 presence is the best confirmatory evidence of the existence 

 of the disease. Sometimes it is necessary, when the organisms 

 are few, to inoculate a guinea-pig. 



Biologic Characters. It grows with difficulty on any of the 

 artificial media. Koch succeeded in growing it on blood-serum. 

 It does not grow in gelatin. It thrives best on 8 per cent, 

 agar or, in the mixture of Roux and Nocard, 8 per cent, 

 glycerin-bouillon. In this bouillon, kept at a temperature of 

 37 C., at the end of from twelve to fourteen days it forms a 

 small pellicle on the surface. Dorsett's egg medium gives very 

 good results. 



In slant cultures of glycerin-agar and blood-serum it grows 

 over the surface of the medium as a dried-up, scaly-looking 

 mass. According to some authorities, it is a spore-bearing 

 bacterium ; others fail to find the existence of spores in it. 

 It is non-motile, though occasionally slight movements have 

 been detected in it. It appears to have no flagella. It is 

 usually killed by exposure to 70 C., but in the dried state 

 may be preserved alive for a considerable time even at a tem- 

 perature approaching 100 C. 



