12 BACTERIOLOGY : 



worm, of favus, of tinea versicolor, may be obtained by removing 

 some of the affected epithelial scales and hairs and examining 

 under the microscope for their respective moulds, after treating 

 with alcohol and ether, and strong caustic potash to remove the 



fat. 



The similarity between different varieties of bacteria is so 

 great, however, and pathogenic micro-organisms are so frequent- 

 ly aped in shape and grouping by the benign varieties, that this 

 first method of diagnosis, as a rule, is merely corroborative to 

 staining and cultural methods. Thus the most noteworthy pe- 

 culiarity of the tubercle bacilli is their resistance to decolorizing 

 agents ; and yet it is also very important that the organisms ap- 

 pear as short rods, with rounded ends, a slight curve and a ten- 

 dency to be arranged in II, V or X like figures. The simple 

 method of diagnosing this bacillus by staining has proved of chief 

 value in tuberculosis of the respiratory tract, the presence of 

 tubercle bacilli in the sputum being practical proof of the ex- 

 istence of the disease. The same method of diagnosing tuber- 

 culosis in other parts of the body has given less satisfaction. In 

 tuberculosis of the genito-urinary tract, it is often difficult to find 

 the bacilli in stained preparations of urinary sediment, and the 

 bacilli are rarely seen in the pus from tuberculous abscesses. Al- 

 though sputum that has become putrid may continue to show the 

 characteristic bacilli, it is advisable to make preparations of fresh 

 fluids. Urine, especially, should be speedily centrifuged and ex- 

 amined, and it is probably an advantage to use a method which 

 obviates certain of the extraneous urinary substances. While the 

 smegma bacillus and the leprosy bacillus resemble the tubercle 



