DIFFERENTIATION OF LEPROSY AND TUBERCLE BACILLI. 228 
methods and considered them satisfactory, though at the same 
time he pointed out various circumstances which might modify 
the result, more particularly the thickness of the sections. 
Wesener repeated Baumgarten’s experiments with tubercular 
material from various sources, and concluded that the methods 
afforded no absolute criterion by which to differentiate the two 
bacilli. Both the methods would stain tubercle as well as 
leprosy bacilli. 
My own experiments point in the same direction. The 
material used was, for the leprosy, chiefly sections of skin 
hardened in alcohol; while the tubercular material consisted of 
cover-glass preparations of sputa, sections of bovine lung very 
rich in bacilli, and human tubercular lung. It may be ob- 
jected that results obtained with bovine tuberculosis are not 
satisfactory, but bovine and human tuberculosis are usually 
considered to be identical in origin, and it was important to use 
sections containing large numbers of tubercle bacilli in order 
to render them comparable with the leprosy sections. It was 
impossible to find specimens of human tuberculosis which con- 
tained sufficient numbers of tubercle bacilli to make the nega- 
tive results certain. 
This question of the number of bacilli present is highly im- 
portant in estimating the rapidity of staining. As is well 
known, the staining properties of bacilli in the same specimen 
vary largely. Some bacilli are stained in a period which is 
quite inadequate to stain others, and the process of decolori- 
sation is also quite gradual. The most striking thing in a 
leprosy section is the enormous number of bacilli present. Now 
even if the two varieties of bacilli stain equally quickly, and are 
exposed to the stain for sucha period as is sufficient to colour 
say 1 per cent. of the bacilli present, it is obvious that the 
leprosy bacilli would appear to stain more quickly and strongly 
than the B. tuberculosis, or even to stain in atime which is 
insufficient to stain tubercle bacilli. The difference is really due 
to the number, and not to the proper staining power of the 
bacilli, Looking first at results obtained with cover-glass pre- 
parations of sputa, it was found that the B. tuberculosis 
