352 THE ALCALIGENES- DYSENTERY TYPHOID 



period varies from five days to three weeks, usually, however, less 

 than ten days. The onset is gradual in some cases, like typhoid, but 

 it may be abrupt with an initial chill, as in pneumonia. The spleen 

 is enlarged, but rose spots are rarely found- The mortality varies; 

 it may be as high as 30 per cent. The postmortem lesions have not 

 been established. In one case the bacillus was isolated from the heart's 

 blood postmortem. Specific agglutinins in the patient's blood serum 

 have not been satisfactorily studied, and the disease as a clinical 

 entity is yet to be defined. The principal evidence of the causative 

 relationship of B. psittacosis to the disease rests at present upon the 

 occasional household epidemics following closely upon the presence of 

 a diseased parrot. 



Immunity and Immunization to Paratyphoid Infection. The duration 

 of immunity following recovery from an attack of paratyphoid fever 

 or of meat poisoning is as yet undetermined. The brilliant results 

 of protective immunization against typhoid fever with vaccines or 

 residues of the typhoid bacillus have led to similar vaccination against 

 paratyphoid infection with polyvalent vaccines composed of the 

 principal strains of the paratyphoid group. Combined protective 

 vaccination against typhoid and paratyphoid by the use of com- 

 pound vaccines has also been attempted. The efficiency of the 

 immunization can not be stated at the present time because statistics 

 are unavailable. 



Dissemination and Prophylaxis. Paratyphoid fever appears to be 

 spread by mild unrecognized cases, by carriers, and by the occasional 

 transmission of bacilli through food, water or milk. Flies may also 

 be a factor in the dissemination of the organisms. Meat poisoning 

 is chiefly disseminated by infected meats, more frequently that of 

 cattle or swine. The customary precautions appropriate for excremen- 

 titious diseases, including the restriction of carriers, may be con- 

 fidently relied upon to prevent the spread of paratyphoid fever. 

 Thorough cooking will largely reduce the occasional danger from 

 contaminated meats. 



