502 APPLICATION OF METHODS OF BACTERIOLOGY 



0.5 c.c. of the above-mentioned emulsion, while the second 

 and third doses are 1 c.c. each. 



As a rule the injections — ^particularly the primary one — 

 are followed by a red, tender, swollen area at the site of 

 puncture. This may be accompanied by headache, fever, 

 general malaise and sometimes by a chill with vomiting or 

 diarrhea. In the majority of individuals the reactions are 

 mild and disappear in from thirty-six to forty-eight hours. 

 In from one to three persons out of every thousand vac- 

 cinated the reaction may be severe, though they are not 

 dangerous. No ill effects of a permanent nature have thus 

 far been noted in about 130,000 persons who have been 

 vaccinated in this country, nor have the vaccinations been 

 seen to influence unfavorably the course of other diseases 

 from which the individual may be suffering. 



It should be needless to say that strict aseptic precau- 

 tions are to be taken in performing the operation. The 

 resistance that is, excited by the vaccination is an "active 

 immunity" — ^that is it is an immunity identical in nature 

 with that acquired by an individual who has recovered from 

 an attack of typhoid fever. In so far as can be stated now, 

 however, the immunity is not permanent. All indications 

 point to its gradual diminution and possible disappearance 

 often in two to three years, so that revaccination after the 

 lapse of this time is advisable. 



Note. — Obtain a pure culture of typhoid bacilli, and 

 from this make inoculations upon a series of potatoes of 

 different ages and from different sources. Do they all 

 grow alike ? 



Before sterilizing render another lot of potatoes slightly 

 acid with a few drops of very dilute acetic acid; render 



