SERUM REACTIONS 199 



dose of serum, but in the immediate reaction rash, 

 pyrexia, joint pains, vomiting, rigors, and occasionally 

 convulsions and collapse occur, either almost immediately 

 or within six hours after the second injection of serum. 

 In the accelerated reaction, these phenomena appear 

 between the eighteenth hour and the fifth day after the 

 second injection of serum. 



The immediate and accelerated reactions may occur a 

 long time after the first course of serum treatment if more 

 serum be given. Goodall records one case in which over 

 four years elapsed between serum treatments for first 

 and second attacks of diphtheria, an accelerated reaction 

 occurring after the reinoculation for the second attack. 



The Arthus phenomenon occurs when a guinea-pig 

 receives several doses of normal horse serum at intervals 

 of some days. Another injection of horse serum then 

 causes an cedematous mass, an aseptic abscess, or an area 

 of necrosis, at the site of the new inoculation, which may 

 be far removed from the region of the previous inocula- 

 tions, and the animal becomes cachectic and dies. 



The Theobald Smith phenomenon occurs when a guinea- 

 pig has been sensitised by a very small single dose of 

 normal horse serum, 0-01 c.c., 0-001 c.c., or even 0-000001 

 c.c. ; if, then, after an interval of twelve to fourteen days 

 a somewhat larger dose of serum, 0-1 c.c., be given, the 

 serious symptoms of hypersensitiveness develop within a 

 few minutes, viz. respiratory failure, paralysis, clonic 

 spasms, and frequently death. At one time it was 

 believed that a small sensitising dose is more effective than 

 a large one in producing anaphy lactic shock, but it has 

 been shown that this is not the case, a large dose merely 

 lengthens the incubation period (up to, it may be, forty 

 days). The reason for this may be that the toxic sub- 

 stance slowly formed by the sensitising dose combines 

 as it is produced with a part of the antigen injected, so 



