TYPHOID FEVER 185 



centimeter of normal blood is about 5, 000,000, 000, and as the red 

 cells and bacteria must be present in the mixture in the same ratio 

 to one another as in the original units of volume, the number of 

 bacteria per cubic centimeter of the vaccine is ascertained according 

 to the equation: 



Number of red cells counted : number of bacteria counted : : 

 5000 millions : x. This method, of course, has no claims to accuracy, 

 as there are too many disturbing factors at play, but it is convenient 

 and has unquestionably come to stay. 



After the strength of the emulsion has been determined the ma- 

 terial is diluted to the desired degree with carbolic acid, such that the 

 final content of the latter shall be between 0.25 and 0.5 per cent. 

 This then constitutes the vaccine and keeps practically indefinitely. 

 The manufacturers now furnish this in little ampules containing the 

 requisite dose. 



Dose and Method of Vaccination. For practical purposes Wright 

 recommends a first injection of 750 to 1000 million organisms, and 

 double this dose for the second treatment. These injections may be 

 made practically anywhere, where the skin is not bound down 

 tightly. I have thus found the outer aspect of the upper arm, 

 where the skin lies quite loose, a favorable locality. Others inject 

 in the loin, or in the back, in the neighborhood of the shoulder-blade. 

 The injections are, of course, to be made with a sterile syringe, and 

 after having cleansed the area to be injected with soap and water 

 and alcohol, or, as has recently been recommended, after painting 

 with tincture of iodin. The needle puncture is covered with 

 collodion. 



Fearing that the injection of a large dose of organisms may at first 

 be followed by a diminution in the protective substances of the body 

 (negative phase), owing to an interaction between the normal anti- 

 bacterial substances and the bacterial antigen, and that the individual 

 may thus be temporarily less resistant to the corresponding infection, 

 Wright has suggested that in persons who are likely to be exposed 

 to typhoid infection soon after the first injection, this should be 

 smaller than usual, and that its effect is to be supplemented later 

 by a correspondingly stronger injection. Whether or not such a 

 danger actually exists in the case of the human being has not yet 

 been demonstrated. In the animal experiments, such a period of 

 diminished resistance apparently does not develop, for Pfeiffer and 



