214 BACTERIA 



Morphology and Stains. Slender rods, generally unbranched, 

 i~5ju long, and 4/4 thick, usually slightly bent; are non-motile, 

 and have no spores or flagella. In old cultures, and sometimes 

 in sputum, branching forms are seen, and, rarely, some that are 

 club-shape. On acid potato, thread forms are found. In the 

 continuity of most of the bacilli, unstained spaces are seen; in 

 others dense deep red granules are found 

 by fuchsin. As this bacillus is difficult to 

 stain, special methods have been devised to 

 demonstrate it, as the sheathing capsule 

 renders it extremely unsusceptible to the 

 ordinary methods of staining. The cause of 

 this resistance is supposed to be a fatty or 



FIG. 64. Tubercle waxy substance in the capsule which is more 

 bacilli in sputum: , , , , , r i < , .,1 * 



stained with fuchsin than probable, because of the fact that stains 



and methylene blue, that are fat selective, such as Sudan III, 

 (Greene's Medical , t* -m i i i i r i 



Diagnosis.) color it very well. Boiling hot carbol-fuchsm 



gives it the best stain. It keeps the color 

 in spite of the action of strong solutions of mineral acids in 

 water, or dilute alcohol. So when tissues, or secretions, are 

 stained with hot carbol-fuchsin for a short time, or cold carbol- 

 fuchsm for a long time, and then treated with a 25 percent 

 solution of HNOa, or H 2 SO4, in water, everything is deprived of 

 the red color, except the tubercle bacilli. All such organisms 

 that are acid proof, are called " acid-fast." There are many 

 other bacilli that have this property. Aniline water and gentian 

 violet solution also stain it. Gram's method dyes the organism 

 violet. Sometimes very young bacilli do not stain at all. 



Vital Requirements. This bacillus thrives best at 37.5C. 

 It grows slowly, is a strict parasite, and an obligate aerobe. In 

 cultures it dies quickly in sunlight, and in diffuse daylight it 

 dies in a few days. It resists drying and light in sputum for 

 months. Its thermal death-point (moist) is 80 C. for ten min- 

 utes; can resist 6oC. for one hour, but succumbs to 05C. in one 



