464 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1915. 



lar to typhoid fever, but milder, occur quite often. These are para- 

 typhoid fevers. They are due to the paratj'^phoid bacilli, of which 

 two principal varieties are described, designated by the letters A and 

 B. These two types are related to each other and also on the one 

 hand to the typhoid bacillus, on the other to a microbe very wide- 

 spread, the colon bacillus, by a series of intermediary forms. The 

 antityphoid vaccines are powerless against these microbes, and a 

 study is now being undertaken to find means of preparing either a 

 single active vaccine for the whole group or a special paratyphoid 

 vaccine. 



It has been thought that, instead of injecting the vaccine under 

 the skin, it would be simpler to introduce it by the digestive tract. 

 This new method is too recent to permit of a final judgment. What- 

 ever its lot may be in the future, it would be hazardous to use it at 

 present; during a war is not the time to begin such an experi- 

 ment. Prudence demands that we use only methods of procedure 

 whose efficacy is indisputable. 



The less the condition of the microbe in use is altered, the stronger 

 and more lasting is the immunity obtained by vaccines. For this 

 reason the heating of cultures has been gradually diminished. At- 

 tempts have been made to replace the heating process by antiseptic 

 substances; and, finally, the systematic use of living cultures has 

 been proposed. 



M. Nicolle advises introducing into the veins living microbes freed 

 from all soluble matter by a prolonged washing. It has been made 

 certain that this method is innocuous and that the bacteria injected 

 remain in the organism and are there destroyed. This discovery is 

 important because it might have been feared that a person vacci- 

 nated, like one having the disease, would throw off living elements 

 and become a source of contamination. This method of procedure 

 admits of numerous applications ; it is successful in giving immunity 

 against cholera, dysentery, and whooping cough, as well as against 

 typhoid fever. 



If we seem to be especially occupied with this last infection it is 

 because its frequency and its seriousness hold first place, especially 

 in our lands. In countries with a warm climate vaccines are fre- 

 quently used against cholera and against the plague. 



The study of anticholera vaccine, begun by Ferran and Gamaleia, 

 has been continued by Haffldne. The living microbe is generally 

 used. On the contrary, Haffkine uses against the plague, cultures 

 sterilized by heating to 70°. 



The immunity created bj^ the passage of an infection or by the 

 introduction of a vaccine is chiefly characterized by cellular modifi- 

 cations which lead to humoral modifications. A vaccine does not act 



