G. W. McCOY 963 



For this purpose, we have found that light-colored guinea pigs show sharper reactions than 

 do the darker animals. 



To remove the hair from the animals, we have employed a depilatory made by mLxing 

 barium sulphide with a saturated solution of sodium sulphide, and adding to this mixture 

 the white of egg and water until it assumed a pastelike consistence. The hair over the abdo- 

 men and the lower part of the thorax is first cut short with scissors. The depilatory is then 

 applied and permitted to remain for a short time (about one to two minutes) when it is 

 scraped off and the part washed thoroughly with running water. The danger of irritation 

 to the parts is minimized by the addition of egg albumen to the paste and by removal of the 

 depilatory as soon as possible. We have found it advisable to prepare the animals twenty- 

 four to forty-eight hours before injecting them, so that any irritation of the skin will have 

 subsided. 



Forty guinea pigs, ranging in weight from 200 to 300 gm., were injected intraperitoneally 

 with 0.1 mgm. of tubercle bacilli. Virulent cultures of the bovine type were used. Eighteen 

 days later 4 of the animals, when injected intracutaneously with 0.02 mgm. of tuberculin 

 of known quality, gave a well-marked reaction which indicated that the animals were sensi- 

 tive. Three days later, or twenty-one days after infection, the remaining 36 animals were 

 divided into six groups of 6 each, and the potency of a different tuberculin tested on each 

 different group. All 6 pigs in all groups received the following amounts of tuberculin: 0.02, 

 CGI, 0.005, 0.002, o.ooi mgm., which were brought up to a total volume of o.i cc. and inject- 

 ed intracutaneously by means of a tuberculin syringe and a short 26-gauge needle. 



Readings were made 24, 48 and 72 hours after the injections, but only those made after 

 48 hours are tabulated, since the reaction reaches its maximum at that time. Degrees of 

 reaction are designated by the figures i, 2, 3 and 4. (4) indicates a very marked reaction, as 

 evidenced by marked redness, edema, necrosis or hemorrhage. (3) and (2) indicate reactions 

 of a less marked redness and edema, depending upon their degree of severity, (i) designates 

 those reactions which show slight redness as well as slight but distinct thickening at the site 

 of injection. 



A comparison of the reactions following the employment of the various doses of 

 the standard (control) preparation and of those under test enables one to judge with 

 fair accuracy of the strength of the preparations being tested. 



The latter method has recently been studied' by the Tuberculin Committee of the 

 Health Section of the League of Nations in comparison with the test tube methods of 

 complement fixation and precipitin formation, as well as with the methods using tu- 

 berculous persons and tuberculous animals. While the conclusion is not to be regarded 

 as final, it was considered that the method of producing intradermal reactions in sen- 

 sitized guinea pigs was the most satisfactory of any of those considered, though it was 

 thought preferable to use the same animals for the standard preparation and for the 

 preparations under test. It is desirable to use white skinned guinea pigs of from 450 

 to 600 gm. 



POLLEN EXTRACTS 



Several procedures are in use for the standardization of these preparations, but 

 probably none gives an accurate index of the value of the preparations as applied to 

 clinical use. Noon^ used as a unit for pollen extracts the material extracted from 



' Cahnette, A., and de Potter, F.: Surle Tilratedes Tuberculins (Societe des nations), Comile 

 d' Hygiene, p. 429. 1926. 



^Noon, L.: Lancet, 180, 1572. 1911. 



