342 AGEICULTUEAL AND INDUSTEIAL BACTBEIOLOGY 



stools within a few weeks after the beginning of con- 

 valescence. Occasionally, however, the bacterium may per- 

 sist for considerable periods of time. This is particularly 

 true when there is an infection of the gall bladder. Such 

 individuals have been known to retain the organisms for 

 many years; they are, of course, much more dangerous in 

 a community even than those who have the disease typhoid 

 in clinical form, inasmuch as they have much greater oppor- 

 tunity to infect drinking water, food, milk, etc. 



Transmission. — It is evident that typhoid fever must 

 most commonly be contracted from drinking water, milk 

 and other foods which have been contaminated. It is prob- 

 able that not infrequently flies may carry the bacteria from 

 the stools of typhoid patients to food. 



Becognition of the Disease. — Typhoid fever is a disease 

 which is not readily differentiated from other diseases in its 

 earliest stages and with difficulty at any time in mild cases. 

 As an assistance to the physician in recognizing the disease, 

 the agglutination or Widal reaction has come into common 

 use. A drop of blood or blood serum from the typhoid 

 patient will usually agglutinate the typhoid bacillus in 

 dilutions of at least 1 to 40, frequently in a dilution of one 

 to many thousand. The disease may also be recognized by 

 planting blood drawn from a vein in broth. 



Prevention of Disease.— The prevention of typhoid fever 

 is accomplished by preventing the access of fecal material 

 to water and food, by the recognition and proper care of 

 patients and carriers, and by the use of vaccines. The latter 

 are necessary probably only where there is danger of the 

 individual drinking water or eating food which has not 

 been properly protected. The vaccine is prepared by grow- 

 ing typhoid bacilli on the surface of agar, washing them off 

 with physiological salt solution, killing by heat, and stand- 

 ardizing to proper dosage. In some cases the' bacteria are 

 dried, ground and mixed with oil to make the so-called 



