HYPERSENSITIVENESS 475 



Passive Sensitization. — Passive sensitization is the transference 

 of liypersensitiveness to a normal animal by injecting blood con- 

 taining specific antibodies obtained from an actively sensitized 

 animal. To be successful it is necessary that blood be obtained 

 from the donor (sensitized animal) at a time when antibodies are 

 ])resent in the general circulation; that a sufficient amount be 

 employ ed to convey hypersensitiveness (this depends upon the 

 concentration of antibodies in the blood) ; and that a normal 

 animal be chosen as a recipient wliose tissues can combine with 

 the donor's antibodies and become hypersensitive to the specific 

 antigen. 



While passive sensitization is best accomplished where the donor 

 and recipient are of the same species, it is well known that blood 

 or serum from different species may be employed. Doerr (1909) 

 and Sherwood and Downs (1928) observed that the sen.sitizing 

 antibodies of one species may in some instances be incapable of 

 sensitizing another species. 



Sherwood and Stoland (1930) found a variation in the recipi- 

 ents of the same species. They transfused four small, healthy 

 dogs of about the same age and weight with equal amounts of 

 defibrinated blood obtained from a large sensitized dog. One of 

 the recipients was rendered extremely sensitive, one was re- 

 fractory (not sensitized) and two were moderately sensitive as 

 judged by the drop in arterial blood pressure. 



The duration of hypersensitiveness produced by passive sen- 

 sitization varies in different species. It persists longer when 

 liomologous immune blood or serum is used than when the anti- 

 bodies are obtained from a different species. Coca (1927) says 

 that wlien a normal guinea pig is sensitized by immune serum 

 from another guinea pig, the former may remain sensitive for 

 sixty to seventy days. If heterologous immune serum is used, 

 the hypersensitivity persists for about ten days only. Coca quotes 

 Friedmann (1909) as saying that passive hypersensitiveness in 

 the rabbit disappears within twenty-four hours, and Richet 

 (1908) as finding that it persists in the dog for twenty days. 



In connection with passive hypersensitiveness, various species 

 exhibit interesting differences in the time between the receipt 

 of antibodies and the development of hypersensitiveness to the 



