When a strain of human tuberculosis was carried from guinea pig to guinea pig by intracerebral inoculation the bacillus of tuberculosis could be readily recovered in the semisolid "Leptospira" medium of Noguchi simply modified by the substitution of guinea pig for rabbit serum. Whether even this modification is required remains to be determined.
The tubercle bacillus in these cultures and possibly in the nervous tissue as well differed from the classical type in that it was less acid-fast and quite lacking in alcohol fastness. However, it retained the Gram stain as modified by Much. Staining reactions, as this culture of the tubercle bacillus shows, are not absolute qualities but are variable with conditions, a consideration which it may be important to recognize. Efforts to define these conditions more precisely are likely to be productive.
