NATURAL AND ACQUIRED IMMUNITY 119 



Fifteen c.c. of i)urciital whole blood will accomplish much of the 

 same effect given intramuscularly. ' ' 



There are a number of reasons why such a program is desirable : 

 (1) experience has shown that severe reactions are least likely 

 to occur when immunization i.s carried out early in life; (2) it 

 gives reasonable assurance of protection before exposure usually 

 occurs; (3) it will probably lead to a larger proportion of the 

 population being immune; (4) it spreads the injections of foreign 

 protein out over a reasonable period of time. 



The question of whether the child has developed immunity in 

 response to vaccination often arises. There is usually little doubt 

 as to whether the vaccination against smallpox is successful and 

 the Schick test is a fairly accurate test for immunity to diphtheria. 

 Many regard the Dick test as a good criterion for scarlet fever im- 

 munity, but this is much more in dispute than the results of the 

 Schick test. In regard to immunity to tetanus, it is possible to 

 determine the amount of antitoxin in the child's blood, but this 

 involves too much time and expense to be made a routine test; 

 hence it is assumed that immunity develops following the injection 

 of tetanus toxoid. There is a great deal of clinical and laboratory 

 data to support this assumption. There is, at present, no way of 

 measuring a child's immunity to H. pertussis although his humoral 

 (antibody) immunity can be measured. Clinical data, however, 

 such as those reported by Sauer (1933) and others support the 

 assumption that immunity results from the administration of his 

 vaccine. It should be borne in mind that the local or systemic re- 

 action to the injection of a bacterial vaccine is no index of either 

 susceptibility or immunity. 



The question is often asked as to why several instead of one in- 

 jection of vaccine is given. There are probabl}^ several reasons for 

 this. Dean and others seem to have shown that in developing 

 humoral immunity, the first one or two injections are the primary 

 stimulus and that to obtain best results, a secondary stimulus 

 should be given about the time the titer reaches its peak, the ob- 

 ject being to let some immunity develop before giving the sec- 

 ondary' stimulus. With bacterial antigens the antibody titer usu- 

 ally rises for 7 to 10 days after an injection while the antibody 

 titer following toxoid is much slower in reaching a peak. Ex- 

 l)erience has shown that a spacing of one to two months is de- 



