26 
Two circumstances led early investigators into wrong conclusions 
as to the viability of the tubercle bacillus. One was this belief that 
the organism contained spores. The other was ignorance of the role 
played by dead tubercle bacilli. Some of the earlier workers spent 
much time in trying to differentiate the resistance of the tubercle 
bacillus with and without spores. These earlier results are still 
quoted, without qualification; in many of the recent text -books and 
writings upon the subject. The notion that the tubercle bacillus 
has a spore is not altogether dead and has created an exaggerated 
idea of its hardiness and resistance. 
THE TUBERCLE BACILLUS AND ITS WAXY SUBSTANCE. 
It was soon found that although the tubercle bacillus does not have a 
true spore, it contains an unusually large quantity of waxy substance 
fats and fatty acid.® It is supposed that these fatty substances sur- 
round the rod, thus affording it a protecting covering. This en- 
velope is supposed to hinder drying and also to protect the bacillus 
against the direct injurious influences of various external agencies. 
The presence of the unusual amount of fatty and waxy substances 
led to a revision of our views upon the subject of the viability of the 
bacillus by placing it in an isolated and intermediate position between 
the spore-bearing and the nonspore-bearing rods. As to just how 
far this view is justified will be discussed subsequently. 
ACID-FAST PROPERTY. 
The difficulty with which the tubercle bacillus takes the basic ani- 
line dyes and the great tenacity with which it holds them are note- 
worth}^. True spores also stain with difficulty and resist the decolor- 
izing action of acids. The analogy between the staining and decolor- 
izing property of spores and the tubercle bacillus is not infrequently 
mentioned in the literature as indicating far greater resistance on the 
part of the tubercle bacillus to heat, dryness, putrefaction, chemicals, 
etc., than is the case with the great run of nonspore-bearing organ- 
isms. Except for the analogy, there is no indication that there is a 
definite relation between the viability of an organism and the ease or 
difficulty with which it stains and decolorizes. In fact, some protozoa, 
certain spirochetes, and other frail micro-organisms stain with more or 
less difficulty or require special technique. 
« Twenty-six and two-tenths per cent according to Hammerschlag; 22 per cent, 
Klebs; 37 per cent, de Schweinitz and Dorset; 20 to 25 per cent, Koch and Aronson; 
from 8 and 10 to 25 and 26 per cent, Ruppel, expressed in terms of alcohol-ether extract . 
This consists of fatty acids and neutral fat and a waxy substance. In contrast to the 
tubercle bacillus, other bacteria contain only 1.7 to 7 and 10.1 per cent alcohol-ether 
extractives. According to Aronson the tubercle wax is, for the most part, not in the 
bacillus, but between the bacilli as a product of secretion. 
