746 TOXINS, TOXOIDS, AND ANTITOXINS 



eight months. Its value is retained when brought to the boiling-point, and is not 

 completely destroyed unless boiled for two hours. 



STANDARDIZATION OF TOXIN 



Toxins can be detoxified or modified into toxoids (anatoxins, Ramon) by forma- 

 lin, iodine, and carbon bisulphide. When detoxified by these agents no reversible 

 reaction has been obtained. A reversible reaction can be obtained when soaps are 

 used as detoxifying agents. The use of soaps was described by Raubischek and Russ' 

 in 1908. They employed sodium oleate. Nelis^ in 1924 reported similar observations. 

 Larson^ in 1924 recommended the use of sodium ricinoleate, on the ground that a 

 purer and more active soap could be easily prepared from castor oil. Aging toxins, 

 i.e., storing in a cool place for a year or longer, modifies much of the toxin into toxoid. 

 B. diphtheriae and B. tetani toxins are very unstable. 



Diphtheria toxin. — If the M.L.D. and the L+ value be determined on a freshly 

 prepared B. diphtheriae toxin and again determined after one year's aging, one will 

 note a 50-60 per cent decrease in the M.L.D. value and only about a 10 per cent 

 decrease in the L+ value. After a year the M.L.D. value remains relatively con- 

 stant, as does the L+ dose. Advantage is taken of this stability in selecting B. 

 diphtheriae toxin for the Schick test (intracutaneous injection to determine antitoxic 

 immunity). It is essential that this toxin for the Schick test remain relatively stable 

 for at least eight months. It is also of importance to use a toxin of high M.L.D. value 

 to reduce the pseudo-reacting substances always present, soluble bacillary products, 

 and other proteins in the toxic broth. 



A suitable stable toxin has a value of at least 300 M.L.D. 's to each mil. This value 

 is too great to allow for the very small accurately measured amount of toxin that is 

 placed in the capillary tube or vial, for the Schick "outfit" which is distributed to 

 the physician. It has been found that two or three volumes of pure neutral glycerin 

 may be added to one volume of the aged toxin without upsetting its stability. Diluted 

 to this extent, the required amount of toxin can be accurately measured into the 

 capillary tube or vial. Each capillary tube or vial is accompanied with a vial con- 

 taining 10 mils of physiological salt solution as the diluent for the toxin. 



Each 0.2 mil of the dilution should contain 1/40 of a guinea pig M.L.D. The 

 Schick test is the intracutaneous injection of this amount in the upper anterior sur- 

 face of the forearm. In those susceptible to diphtheria an area of erythema develops 

 within twenty-four to forty-eight hours, lasting four to five days, and gradually dis- 

 appears, leaving a definitely circumscribed scaling area of brownish pigmentation. 

 A pseudo-reaction may occur due to a local hypersensitiveness of the tissue cells to 

 the proteins in the toxin dilution. This reaction is commonly urticarial in character; 

 it appears within eighteen hours and as a rule disappears on the third or fourth day, 

 leaving a poorly defined area of reddish-brown pigmentation without scaling. Indi- 



' Raubischek, H., and Russ, V. K.: Ztschr.f. Imnmnitdlsforsch. u. expcr. Therap., Orig. I, i, 395. 

 1908-9. 



' Nelis, P.: Compt. rend. Soc. de bioL, 91, 1159. 1924. 



3 Larson, W. P., and Nelson, E.: Proc. Soc. Exper. Biol. &* Med., 21, 278. 1924; Larson, W. P., 

 Evans, R. D., and Nelson, E.: ibid., 22, 194. 1924. 



