136 SPECIAL BACTERIOLOGY 



their relation to lymphangitis and not to glanders, the bacillus of 

 glanders being, moreover, absent. 



TUBERCULOSIS. 



The infectious nature of this disease was first demonstrated by 

 Villemin -in 1865, when he communicated the disease to healthy 

 experiment animals with tuberculous material. Cohnheim confirmed 

 these experiments by inoculations into the anterior chamber of the 

 eyes of experiment animals. In 1882 Koch discovered the Bacillus 

 tuberculosis, which is now known as the cause of mammalian tuber- 

 culosis. 



Microscopical Appearances. Koch's bacilli are small, thin rods, 

 varying in size from 0'2 to 0*4 /x, broad, to 3 to 4 p long; they are 

 slightly bent, generally occur singly, but in cultures sometimes form 

 chains of four to six individuals ; in rare cases they exhibit a club-like 

 swelling at one end and branches, whereby a certain relationship with 

 the actinomyces group has been ascribed to them. 



Motility. Non-motile. 



Spore Formation. The clear spaces present in stained specimens 

 have been described by some authorities as spores, and by others as due 

 to degenerative processes. 



Staining Reactions. The bacilli stain with difficulty, but once they 

 are stained they retain the dye with great tenacity. The results with 

 the Gram and Cladius staining methods are positive. For the special 

 methods of preparing and staining cover-glass specimens and sections 

 see Technique, 13, 14, 40. 



According to Koch's recent investigations, tubercle bacilli contain 

 two solid fatty acids, one of which is soluble in reduced alcohol and 

 saponified by caustic soda ; the other is not saponified, and is only soluble 

 in boiling absolute alcohol and ether. Both of these fatty acids are 

 stained by the specific tubercle bacilli stains ; but by the process of 

 decolorization, the one soluble in alcohol gives up the stain, while the 

 other retains it ; thus the acid fixes the staining material and accounts for 

 the staining reaction (see Photomicrograph of tubercle bacilli in sputum, 

 Fig. 47). It is possible with a warm solution of caustic soda to remove 

 the fatty acids out of the body of the bacilli, and observe by a micro- 

 scopical examination how they pass out in the form of colourless drops, 

 and coalesce into larger drops. According to Koch, these fatty acids 

 form a continuous layer in the bodies of the bacilli, thus providing them 

 with a protection against external influences. 



This peculiar micro-chemical staining reaction found in the case of 



