VACCINATING INJECTION 77 



antibody; and it follows that the anaphylactic state is 

 only slightly diminished. 



If we carry out a series of graduated small injec- 

 tions, we end in neutralising the sum total of the 

 sensibilisin in the circulation; thus desensitised, the 

 subject acquires that anti-anaphy lactic immunity 

 which is pecuHar to every normal individual. 



In order to effect this immunity it is therefore in 

 our interest, for the purpose of vaccine, to inject as 

 much antigen as possible, without, however, injecting 

 too much, for anaphylactic shock supervenes very 

 rapidly. 



When should we stop ? What is the optimum 

 dose of antigen that should be injected ? To this 

 question, which has often been put to us, the reply 

 is as follows: To be certain that anti-anaphylactic 

 immunity is acquired it is necessary to proceed to 

 the dose which we term " precritical," the effect of 

 which is shewn in man by an onset of anxiety and 

 a redness of the face lasting some minutes. It is a 

 sure indication, and from this point of time onwards 

 the patient is desensitised, and is in a position to 

 tolerate with impunity as much serum as it is desired 

 to administer. 



This precritical dose may be varied in different 

 subjects according to the degree of hypersensitiveness 

 manifested by the particular individual. The prin- 

 ciple is that we should act in practice as if we were 

 always deaUng with individuals who are most hyper- 

 sensitive; and commencing with weak doses, as above 

 indicated, proceed rapidly without stopping if we 

 see that the patient does not react to them, and go 

 on injecting stronger and stronger doses till the 

 precritical dose is attained. 



