DIAGNOSIS OF TUBERCULOSIS 449 



it can be frequently demonstrated or at least inferred by an increase 

 of local clinical signs. The local reaction at the site of inoculation 

 consists essentially of a reddened, swollen, circumscribed area of 

 inflammation. The specificity of the reaction is dependent upon the 

 size of the dose of tuberculin. Too large a dose may cause a reaction 

 even in a non-tuberculous subject. It is obvious that patients already 

 exhibiting a febrile reaction due to intercurrent disease or otherwise 

 are unfit subjects for injection, for the rise in temperature is the chief 

 diagnostic symptom relied upon in establishing a diagnosis. 



The subcutaneous injection of old tuberculin is used only for adults 

 and for children over five years of age in the very early stages of the 

 disease. This reaction is claimed by some observers to be more deli- 

 cate than any other tuberculin test. In practice tuberculin is intro- 

 duced subcutaneously either in the breast or preferably in the back, 

 and a control inoculation, using dilute glycerin containing 0.5 per 

 cent, carbolic acid, is made in another area. If a nodule and con- 

 gestion appear at the site of inoculation of the tuberculin and the 

 control area remains practically unchanged, the reaction is considered 

 positive if the temperature chart taken at half-hour intervals shows 

 at least half a degree rise in temperature above that exhibited pre- 

 viously for several days. The size of the dose to be administered 

 depends upon the age and condition of the patient and upon the 

 potency of the old tuberculin. 



(6) The Cutaneous Test (von Pirquet). The patient's forearm is 

 sterilized and two drops of undiluted old tuberculin are placed upon 

 the skin about 8 to 10 c.m apart. A light scarification is made, pre- 

 ferably with the von Pirquet scarifier, through each drop of tuberculin. 

 A control scarification is made midway between the drops, but no 

 tuberculin is applied here. A small pledget of cotton is placed over 

 each drop of tuberculin and allowed to remain ten minutes to prevent 

 the tuberculin from spreading beyond the site of scarification. The 

 amount of cotton used should be small enough to prevent any con- 

 siderable absorption of the tuberculin. No dressing is required. Dur- 

 ing the first few hours of vaccination the control and vaccinated areas 

 appear the same, a slight area of inflammation due to trauma sur- 

 rounding each. The specific reaction appears first as a slightly 

 elevated red area around each drop of tuberculin, which increases in 

 size and somewhat in elevation until it reaches a diameter of from 

 1 to 3 or even 4 cm., the former being the more common. The 

 maximum intensity is usually reached within forty-eight hours, the 



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