12 LOCAL TISSUE REACTIVITY 



that ihc essential leatiire ^vhich caniK^t possibly escape observa- 

 tion, histologically and in the gross, is the hemorrhage following 

 the intravenous injection, riie readings ot the reactions recorded 

 in this monograph are based on this essential ieatine and are 

 only made in rabbits surviving lor at least tour hours folloAving 

 the intravenous injection ol reacting factors. 



If the animals die ^vithin the first four hours following the in- 

 jection of a bacterial filtrate, the reading of the reaction is im- 

 possible in most instances. The reaction may diffuse through the 

 skin of the a])dominal wall, and assume a livid appearance which 

 is very diflicult to interpret. Only occasionally it is possible to 

 observe well dehned hemorrhagic reactions in dead rabbits. It 

 seems advisable, therefore, to disregard the readings of rabbits 

 which die 'within the fh\st four horns follo"\ving the injection. 



As a rule, the reactions of siu\iNing rabbits become visible in 

 the gross as early as one-half to one hotu' after the intravenous 

 injection. In typical strong reactions the early appearance is that 

 of a crop of petechiae ^^■hich continuously increase in size until 

 there results an extensive confluent hemorrhaoe forming" a sac 

 filled ^vith blood. The color rapidly changes from blue to violet 

 and almost black. There is an angry red zone at the periphery. 

 The entire process may be so rapid that the petechial stage is 

 indistinguishable in the gross. 



With highly diliued preparations, Aveak reactions may be de- 

 layed in appearance, i.e., ten to t^vehe hours instead of the custo- 

 mary foiu' to five hours. Some ^veak reactions may appear promptly 

 but disappear the folloAving day. The reactions of this type may 

 be best described as punctiform. They appear as a crop of petechiae 

 "^vhich do not become confluent and have a tendency to fade 

 promptly. Sometimes follo^ving the intra\enous injection one 

 may see an accentuation of preexisting swelling and erythema. 

 In imminiological studies concerning this phenomenon, Avhen the 

 record of the results is based in most instances on the appearance 

 of the reaction in the gross, weak reactions should be considered 

 as doubtfid and not much, stress laid upon them, since they may 

 only present a mere accentuation of a primary inflammatory re- 

 action and not be an expression of the phenomenon of local skin 

 reactivity to bacterial filtrates according to the present conception. 

 Inasmuch as the skin preparation is elicited by means of an 

 intradermal injection, the reaction is well defined in the super- 

 ficial layers of the skin and penetrates, in many instances, into the 



