DIAGNOSIS OF TUBERCULOSIS 493 
large volumes of urine and injecting the sediment into guinea-pigs 
is the most practical method of detecting tubercle bacilli in this 
excretion, for it rules out both the Lustgarten and smegma bacilli, 
which do not produce lesions in guinea-pigs. The slight differences 
in acid- and alcohol-fastness between these organisms and the tubercle 
bacillus make diagnosis by the direct smear method of doubtful value. 
i^ece*.— Tubercle bacilli may appear in the feces either because they 
have been swallowed with the sputum or because of the existence of 
tuberculous ulcers in the intestinal tract.^ Acid-fast bacilli which are 
not true tubercle bacilli are quite common in the feces, and for this 
reason animal inoculation after treatment of the feces with antiformin 
is the best method for demonstrating the organism. 
ilfzY/:.— Tubercle bacilli are very infrequent in human milk, although 
they are said to be relatively common in unpasteurized cow's milk 
as it is sold in large cities. The organisms get into the cow's milk far 
more frequently through the contamination with feces than from 
direct infection through the udder. Microscopic examination of 
the sediment of milk or cream is usually valueless, as is the examina- 
tion of the cream layer itself. Acid-fast bacilli which are not tubercle 
bacilli very frequently cause confusion. Among these organisms are 
those described by Petri and Rabinovitch, which are called butter 
bacilli. Inoculation of the sediment and of the cream of milk into 
guinea-pigs is the only safe test. 
Immunity and Immunization. 2— The disproportion between the inci- 
dence of "healed tubercles" in cadavers which do not exhibit symp- 
toms of tuberculosis antemortem and the actual number of clinical cases 
suggests that the average individual possesses a certain degree of 
refractoriness to progressive invasion by the tubercle bacillus; that is 
to say, the clinical cases of tlie disease are considerably outnumbered 
by those in whom the organism has gained entrance, but failed to 
develop sufficiently to cause symptoms. Early, uncomplicated cases 
of tuberculosis frequently react favorably when placed in a favorable 
environment. Spontaneous recovery from tuberculosis complicated 
by secondary infections with other bacteria is more tedious and the 
prognosis is generally less favorable. 
Active immunization of man with various products of the tubercle 
bacillus has been one the greatest problems of medicine. Up to 
the present time the solution of this problem has not been realized. 
At least a generation must elapse before final judgment can be passed 
upon any system of human immunization, for the disease tuberculosis 
progresses slowly and results to be trustworthy must be numerous and 
of long duration. 
' See Laird, Kite and Stewart (Jour. Med. Res., 191.3, 29, 31) for summary and 
literature. 
2 For an excellent summary of Immunity in Tuberculosis see Baldwin (Am. Jour. 
Med. Sci., 1915, 149, 822). 
