THE INFECTIOUS DISEASES. 



247 



FIG. 121. TUBERCLE BACILLI IN SPUTUM FROM A 

 CASK OF PULMONARY TUBERCULOSIS. 



Showing the bacilli stained with fuchsin and pus cells 

 stained for contrast with methylene blue. 



when stained often presents an irregular beaded or knobbed appearance, due to an un- 

 evenness in the coloring of the protoplasm, or to involution changes. It is immobile 

 and spores have not been demonstrated 

 in it, 



At the temperature of the body it 

 can be grown on many of the artificial 

 culture media. 



The growth of the tubercle bacillus 

 in cultures is very slow in comparison 

 with that of most of the pathogenic 

 micro-organisms. After several weeks' 

 growth it forms dry, scaly masses or 

 thin, wrinkled pellicles on the surface 

 of the media (Figs. 122 and 123). It 

 requires a certain amount of oxygen for 

 its growth, and thrives best in the dark. 

 It is killed by an exposure of a few 

 hours to direct sunlight, or if moist is 

 killed by an exposure of from ten to 

 fifteen minutes to 70 C. On the other 

 hand, it may long retain its vitality in 

 the dried condition. 



Cultures can be continued indefi- 

 nitely from generation to generation with 

 a slowly diminishing virulence which 



finally is largely lost. Under certain conditions the virulence may be restored or en- 

 hanced by successive inoculations into susceptible animals. 



The tubercle bacillus does not, so far as we know, grow in nature outside of the 

 bodies of men and certain warm-blooded animals. It is thus apparently strictly parasitic. 



Methods of Staining the Tubercle Bacillus. 



IN FLUIDS. For the examination of fluids, such as sputum, 1 etc., the material 

 should be spread in a thin layer on a cover glass, dried in the air, and then passed thrice 

 through the flame (see page 153). 



While, as has been said above, the tubercle bacillus is stained much less easily with 

 the anilin dyes than are most bacteria, it can be deeply colored by the use of accessory 

 agents which intensify the stains or render the protoplasm of the bacilli more accessible 

 to them. But when once stained the tubercle bacillus clings with great tenacity to its 

 color in the presence of the usual decolorizing agents. 



A variety of methods are in vogue for staining the tubercle bacillus, most of them 

 being more or less unessential modifications of the original process formulated by Koch 

 and Ehrlich. Ziehl's solution is among the most useful. This is made by adding to a 

 five-per-cent aqueous solution of carbolic acid about one-tenth its volume of saturated 

 alcoholic solution of fuchsin. This carbolic fuchsin will keep unchanged for a long time. 



The prepared cover glass is floated in a watch glass or porcelain capsule specimen 

 side down on this coloring fluid, and gently heated almost to boiling for from three to 

 five minutes. 



The entire specimen is thus completely stained, tubercle bacilli, tissue elements, and 

 other bacteria which may be present, all in the same way. The next step is to remove 

 the color with acid from all the structures which may be intermingled with the tubercle 

 bacilli ; the latter, owing to the tenacity with which they retain the color, being but 

 slightly affected. This is done by dipping the cover glass into an aqueous or alcoholic 

 solution of five-per-cent sulphuric acid, and shaking it about -for a few seconds. Under 



1 It is well in obtaining sputum for examination in cases of suspected pulmonary 

 tuberculosis to secure that which has been raised during several hours, including the 

 early morning discharge. 



