REACTIVITY TO VARIOUS MICROORGANISMS 59 



lire to induce the phenomenon of local skin reactivity to diph- 

 theria toxin in rabbits. 



Recently Freund (1934c/) attempted the experiment in guinea 

 pigs. The preparation consisted of an intradermal injection of 0.1 

 c.c. of diphtheria toxin in various dilutions ranging from 1:250 

 to 1:2500; 0.0016 c.c. of the toxin employed by him contained 

 1 M. L. D. B. tyjjJiosus "agar Avashings" filtrates in doses from 

 0.5 c.c. to 1 c.c. were injected intra\enoiisly, t^venty-four hours 

 later. Some of the guinea pigs prepared by dilutions in the range 

 of 1:250 to 1:750 showed primary hemorrhagic lesions before the 

 intravenous injection of the B. typJiosus filtrate {i.e., twenty-four 

 hours after the intradermal injection) . In one guinea pig the in- 

 travenous injection of B. typliosus filtrate seemed to have en- 

 hanced the primary hemorrhagic lesion. A few guinea pigs which 

 shoAved no reactions to diphtheria toxin in twenty-four hours be- 

 came hemorrhagic later incidentally to the intra\enous injection 

 of B. typhosus filtrate. 



It is well known that the intradermal injections of diphtheria 

 toxin produce primary hemorrhage and necrosis w^hich fully de- 

 velop w^ithin forty-eight to seventy-t^vo hours follo^ving the in- 

 jection. Freund concluded from his experiments that diphtheria 

 toxin in the guinea pigs acts as a skin-preparatory factor. It should 

 be noted, howexer, that the doses employed by Freund \\ere con- 

 siderably larger than the amount necessary to elicit the primary 

 hemorrhagic and necrotic reactions. 



According to Kellogg (1922), I/40 of a unit is the minimal 

 amount producing a primary hemorrhage and necrosis in the 

 guinea pig upon intradermal injection. As is seen from the de- 

 scription of Freund's experiments, reactions ^vere obtained only 

 with dilutions ranging from 1:250 to 1:750 {i.e., 1/4 M. L. D. to 

 1/12 M. L. D.) but no reactions Avere obtained with dilutions 

 ranging from 1 : 1000 to 1:25,000 (notably doses consisting of 1 17 

 of M. L. D. to 1/425 M. L. D.) . It is obvious, therefore, that the 

 reactions described by Freund could have been entirely due to the 

 primary effect of the diphtheria toxin and apparently not related 

 to the phenomenon under discussion inasmuch as the reactions 

 appeared ^vithin the time most siiital)le for the appearance of pri- 

 mary diphtheria toxin reactions, and ^vere produced only by doses 

 capable of eliciting primary reactions. 



