16 IOWA ACADEMY OF SCIENCE 



With the view of determining the factors responsible for the im- 

 munity and the extent of the protection, we made a series of examina- 

 tions of forty-six medical students whom we vaccinated three months 

 ago. 



Technique of preparation and administration of vaccine ; — The vac- 

 cine consists of a culture of typhoid bacilli killed by exposure for one 

 hour to a temperature of 56° C. and the addition of 0.25% trikresol. 1% 

 is injected into the subcutaneous tissue of the arm by means of a 

 hypodermic syringe in three doses given at intervals of ten days — 

 the first dose consisting of 500,000,000 typhoid bacilli and the other 

 two of 1,000,000,000 each. 



Reaction; — In four to five hours after injection, the site of inocula- 

 tion becomes red, swollen and tender and remains so, usually for sev- 

 eral days. About the same time general symptoms in the form of head- 

 ache, malaise, slight fever, etc., also usually develop. These, however, 

 always disappear within 48 hours. 



The reactions which indicate immunity can, however, onlj^ be deter- 

 mined by an examination of the blood-. These may be divided into 

 the following: 



1. Leucocytic — In about two hours after the injection, the number 

 of white corpuscles of the blood becomes markedly increased — rising 

 from the normal of about 7,000 to 15,000 or 20,000. The increase con- 

 sists at first principally of polymorphonuclear neutrophile leucocytes 

 but after several days principally of the large mononuclear type. The 

 leucocyte count of the blood returns to the normal in about four days. 

 The leucocytes appear to be associated with the production of the more 

 specific immune bodies. 



2. Phagocytosis, which refers to the ingestion of foreign material, 

 such as bacteria, by leucocytes, is increase from one or two thousand 

 times. 



3. Agglutinins, the substances which cause the bacteria to lose their 

 motility and to gather in small clumps, is also increased from 100 to 

 1,000 times the amount found in normal blood. These are of a specific 

 nature, i. e., if induced by typhoid bacilli will react only on typhoid 

 bacilli. They are the basis of the Widal test for typhoid fever. 



4. Bacteriolysins, or substances that actually destroy bacteria, are 

 also increased, but our present means of determining the quantity of 

 such is very unsatisfactory. 



Just how long the specific antibodies remain in the system is not 

 known. The phagocytic index and the quantity of agglutinins is still 



