CAUSING CHRONIC INFECTIONS. 
99 
cellular or soluble toxin, to which is attributed the 
fever, headache, loss of appetite and so on, and an en¬ 
dotoxin which causes an irritation of the tissues lead¬ 
ing to the formation of the tubercle. The absorption 
of these toxins causes the formation of anti-bodies but 
not in sufficient amount to cause immunity. The toxins 
of the tubercle bacilli may be obtained from cultures, 
and are used under the name of tuberculin in the diag¬ 
nosis and treatment of the disease. The tuberculin re¬ 
action used in the diagnosis is based upon an observa¬ 
tion made by Professor Koch, that animals having 
tuberculosis were very sensitive to the poison, and 
when injected with even a small amount of tuberculin 
developed fever, headache, nausea, vomiting, and gen¬ 
eral malaise, while the diseased tissues became tempor¬ 
arily more inflamed. Healthy animals were unaffected. 
This method has been employed among tuberculous 
patients, using from i to io milligrams of the tuber¬ 
culin subcutaneously. Simpler methods have more re¬ 
cently been used, such as the von Pirquet test, in which 
the tuberculin is introduced into the superficial layers of 
the skin with a scarifier, and the Moro test, in which 
the tuberculin is rubbed in, in the form of an ointment. 
In the first method a positive reaction is manifested by 
fever, headache, and so on, as described above, but in 
the cutaneous tests there is only a local redness about 
the point of inoculation. A positive test means that 
tuberculosis is present in the body, but it does not tell 
us where or whether it is active or not. In children, a 
positive reaction usually means active disease. 
Tuber¬ 
culin 
reaction 
