CHAPTER XX 

 THE TUBERCLE BACILLUS 



The tubercle bacillus occurs in air, dust, soil and water as a result of con- 

 tamination with feces, urine, sputum or other discharges from tuberculou- 

 animals. It is frequently present in the milk of tuberculous cows and in prods 

 ucts made from it, such as butter and cheese. Muscle tissue is rarely involved, 

 but tubercle bacilli are numerous in the glands, lungs and viscera of diseased 

 animals. Through contamination by dust and dirt and handling by tubercu- 

 lous individuals, various articles of clothing and food are polluted with tubercle 

 bacilli. 



It is believed that bed-bugs inhabiting the bed of a tuberculous patient 

 acquire tubercle bacilli, harbor them for long periods, and, when opportunity 

 occurs, bite people and in so doing, infect them. 



This organism has a wide distribution in every climate and may enter man 

 through the respiratory tract, by inhalation, through the gastro-intestinal 

 tract, by food, especially raw milk, possibly through the genital organs, by 

 sexual intercourse, and through infection of wounds. In the great majority of 

 cases, tuberculosis in man follows infection through the respiratory tract, 

 of the rest most infections in man are by way of the intestinal tract. 



Morphology. Tubercle bacilli usually appear as small, straight or curved, 

 solid-staining or beaded rods, 1.5 to 4.0 M long and 0.3 to 0.5 ^ wide. They may 

 be arranged singly or in irregular clumps. Organisms removed from old cul- 

 tures are often larger than those found in tissue and frequently show branching. 

 Beaded forms of tubercle bacilli may look like several small cocci in a row. 



Staining. The peculiar reaction of the tubercle bacillus to stains, acids 

 and alcohol facilitate the recognition of this organism microscopically. With 

 the exception of the leprosy bacillus it is probably the only organism which is 

 both acid- and alcohol-fast. Presumably on account of its fatty capsule, the 

 usual anilin stains penetrate it with difficulty or not at all. When stained with 

 carbol fuchsin neither acid nor alcohol decolorizes it and other stains cannot 

 tint it. 



Of the many methods of staining for the tubercle bacillus the following two 

 are probably the best: 



1. Stain with carbol fuchsin for 15 minutes or longer. 



2. Immerse in Pappenheim's solution for 15 minutes, or until the slide 

 looks blue. 



3. Wash in water. 



4. Dry and examine. 



1. Stain with carbol fuchsin for 15 minutes or longer. 



2. Wash with 5 per cent, aqueous solution of nitric acid until bleached 

 (i. e., pale pink). 



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