DIAGNOSIS OF TUBERCULOSIS 495 
the disease. A peculiar and characteristic type of infection of cattle, 
known as Perlsucht or pearly disease, which progresses slowly and is 
recognizable only in the later stages, is distinguished by the occurrence 
upon serous surfaces of thick fibrous tumors containing much con- 
nective tissue. The lesions in infections of the peritoneal surfaces 
consist of large numbers of solitary or clustered tubercles varying in 
size from 1 to more than 10 mm. in diameter. They may be attached 
to the surface by tough, fibrous pedicles or they may rest directly upon 
the membrane itself. These tumors may become calcified or caseated 
and they are larger than tubercles found in human tissues. Morpho- 
logically their structure is fundamentally not unlike human tubercles. 
Theol)ald Smith^ was the first to clearly point out the diflerences 
between the human and bovine tubercle bacilli. His evidence was 
based upon morphological, cultural and pathological characters. He 
showed that the human tubercle bacillus, grown on serum, was longer 
and slenderer than the bovine type and freciuently curved. The growth 
is more luxuriant, forming a thick, wrinkled membrane upon glycerin 
broth. The bovine type commonly develops feebly in this medium 
and produces a thin, delicate pellicle. The reaction curves of the 
two types on glycerin broth are distinctive and characteristic. The 
bovine type gradually creates an alkaline reaction; the human type 
leaves the reaction acid, and tuberculin made with the bovine type 
consequently is alkaline in reaction; that of the human type is acid.^ 
The pathogenic action of the two types is distinctive; the bovine type 
is highly pathogenic for rabbits and calves; the human type is only 
slightly pathogenic for these animals. One milligram of a human 
culture fails to kill rabbits, but 0.1 mg. of a freshly isolated bovine 
culture results fatally. 
The important differential characters are summarized in the follow- 
ing table: 
Human Types. Bovine Types, 
morphology. 
On serum or glycerin bouillon, long, slen- On serum or glycerin bouillon, relatively 
der, slightly curved rods which usually short thick rods irregularly arranged; 
stain uniformly; occur in clusters usu- frequently exhibit slight irregularity in 
ally lying parallel. staining. 
CULTURAL CHARACTERS. 
Glycerin bouillon, after two to four weeks' Glycerin bouillon, delicate membrane ex- 
growth, dense wrinkled membrane. hibiting occasional wrinkling of the 
surface. 
Reaction remains permanently acid. Reaction gradually becomes alkaline. 
Tuberculin has acid reaction. Tuberculin has alkaline reaction. 
Growth on blood serum relatively luxur- Growth on blood senmi relativ^ely meagre 
iant and develops with comparative — develoi)s slowly. 
rapidity. 
ANIMAL PATHOGENE.SIS. 
Guinea-pigs very susceptible; young Guinea-pigs, young cattle, rabbits and 
cattle, rabbits and swine resistant to swine very susceptible to infection, 
infection. 
1 Jour. Exp. Med., 1898, 3, 451. 
2 See Kendall, Day and Walker: Jour. Infec. Dis., 1920, 26, 4.5, 77. 
