274 PUBLIC HEALTH BACTERIOLOGY 



showing these have no increased resistance against heat 

 and disinfectants, the spore interpretation is probably 

 incorrect. The beads or highly stained portions have 

 likewise been called spores, but the whole matter is at 

 present unsettled. 



The tubercle bacillus stains imperfectly or not at all 

 with ordinary watery aniline dyes, and only after long 

 exposure or heating, or more quickly if a mordant is used. 

 Once stained, the bacilli retain the dye tenaciously, in 

 spite of treatment with alcohol or strong acids, and for the 

 latter reason they are spoken of as " acid-fast " bacilli (acid- 

 proof would be a better term). This feature seems to be 

 due to the presence of fatty substances in the cell, and 

 has furnished the basis for differential staining methods. 

 The fatty substances are really wax-like in nature, and are 

 soluble in alcohol + ether. 



B. tuberculosis is non-motile, non-nagellar, non-sporing, 

 does not grow on gelatin, and is Gram -positive. Recently 

 varieties have been described which are not acid-fast, but 

 are stained by Gram's method prolonged, and these forms 

 are stated to be present in old tuberculous lesions, where 

 the ordinary form is not found and yet the material is 

 virulent. These are, (i) A fine bacillary form, often 

 showing granules, and (2) Free granules. Much also 

 found that when acid-fast forms were added to milk 

 (sterilized) and incubated, the acid-fast forms disappeared, 

 and yet when the milk was injected into an animal, tuber- 

 culosis was produced and in the lesions acid-fast bacilli 

 were demonstrable. If these statements are conclusively 

 proved, they are of the first importance. 



Chemical Analysis of Tubercle Bacilli. Water 85-9 per 

 cent, solids 14-1 per cent. The ash shows 55 per cent of 

 P 2 5 , 12-6 per cent of CaO, 11-5 per cent of Mg, 13-6 per 

 cent of Na 2 0, 6.3 per cent of K 2 0. 



Cultures. The bacillus is not easily cultivated ; growth 

 fails, or is slow or scanty ; fails on agar and gelatin entirely, 

 but on glycerin agar (3 to 6 per cent) and in glycerin broth 

 (6 per cent) growth takes place in ten to fifteen days, 

 becoming visible first as dry white spots, the extension 

 and fusion of which form a dull, whitish, wrinkled pellicle 

 or layer. These media are suitable for subcultures ; for 



