ESMOND R. LONG 1017 



nets. Shortly after his first description of tuberculin,' he established as a standard of 

 suitable potency a tuberculin of which 0.5 cc. or less would kill in from six to thirty 

 hours, with characteristic pathological change, a guinea pig infected one month previ- 

 ously with tuberculosis. Various other standardizing procedures have been devised, 

 which I have reviewed elsewhere.^ The ideal standardizing procedure would be quan- 

 titative chemical determination of the active principle present. As this is at present 

 impossible in complex preparations, I have developed a biological method with a stand- 

 ard unit, which is accurate, although admittedly cumbersome. 



The basis for this method is the guinea pig testicle reaction which I first de- 

 scribed in 1924.3 This is an allergic reaction of the same biological type as the skin and 

 lethal dose tests, but more specific and more delicate. In experiments on tuberculous 

 infection of the testicle in the guinea pig I found' that the normal-appearing testicle 

 of the tuberculous guinea pig is extraordinarily sensitive to tuberculin, minute doses 

 causing profound degeneration and ultimate absorption of the germinal cells, the sper- 

 matocyte being the one primarily affected. Doses a thousand times as large are with- 

 out effect upon the testicle cells of the normal guinea pig. The complete details of 

 this specific test cannot be given here, but the reader is referred to an article- on the 

 assay of tuberculin on the basis of the spermatocyte reaction; and to Figure i, taken 

 from the same article, which illustrates the practical measurement of the spermato- 

 cyte unit of tuberculin, i.e., that amount of tuberculin causing complete abolition of 

 spermatogenesis. 



This method is on trial in a number of laboratories concerned with large-scale 

 usage of tuberculin. Until its usefulness or that of a better method is demonstrated 

 the view of Baldwin, Petrofif, and Gardner^ may be considered sound, viz., that a 

 constant, standard method of preparation is most important, with recognition of the 

 individual variation of patients in sensitiveness. 



TYPES OF TUBERCULIN REACTION IN USE 



In practice, tuberculin, which is employed both diagnostically and therapeuti- 

 cally as described below, is used in a great variety of ways. The most common means 

 of administration are: (i) subcutaneous injection, i.e., injection with a hypodermic 

 syringe into the subcutaneous tissue where absorption is rapid; (2) the cutaneous 

 method of von Pirquet, in which a drop of tuberculin is allowed to dry on a freshly 

 scarified point of skin; (3) the intracutaneous test of Mantoux and others, in which a 

 small amount of tuberculin is injected through a fine hypodermic needle (26 or 27 

 gauge, short length) parallel to the surface, lumen of the point up, into the most super- 

 ficial layer, a white bleb of blanched skin indicating proper injection; (4) the ophthal- 

 mic test developed independently by Calmette and by Wolff-Eisner, in which a drop 

 of tuberculin or a disk impregnated with tuberculin is placed on the ocular conjuncti- 

 va; and (5) the percutaneous method of Moro, in which a salve made up of tuberculin 

 and lanolin is rubbed into the skin. The first and fifth are commonly used in treat- 

 ment, and the other three, leading to local reactions at the point selected, in diagnosis. 



^ Koch, R.: op. cit., 17, 1189. 1891. 



== Long, E. R.: /. Infect. Dis., 37, 368. 1925. 3 Long, E. R.: Ain. Rev. Tuberc, 9, 215. 1924. 



"Baldwin, E. R., Petroff, S. A., and Gardner, L. U.: loc. cit. 



