392 TYPHOID FEVER 



the animals from which the meat was derived have been suffer- 

 ing from illnesses probably due to the organisms subsequently 

 found, but this has not always been the case, healthy meat being 

 here contaminated by contact with infective matter. The foods 

 giving rise to poisoning usually belong to the preserved food 

 class, or consist of sausages or similar products, but cases also 

 arise from infected milk. There is every reason to believe that 

 the organisms in question may not be killed in the ordinary 

 processes of cooking, in which the internal parts of the meat 

 may not reach the temperature of blood coagulation. 



The organisms included in the paratyphoid and food-poisoning 

 group are as follows : The bacillus paratyphosus, varieties A 

 and B, originally isolated from pathological conditions in man ; 

 bacillus enteritidis Gaertner, isolated from meat-poisoning cases ; 

 bacillus ^Ertryck, also isolated from meat poisoning ; bacillus 

 suipestifer (Salmon's bacillus of hog cholera, which is probably 

 identical with b. yErtryck) ; psittacosis bacillus, occurring in a 

 disease of parrots ; bacillus typhi murium, isolated by Lomer 

 from an epidemic of enteritis in mice ; and Danysz's bacillus, 

 isolated from an epidemic in field mice, and used by him for 

 originating epidemics in rats. The pathological effects produced 

 by these organisms include, on the one hand, general septicsemic 

 manifestations, and, on the other, gastro-enteritis. The chief 

 members of the group will be described below. 



The Characters of the Bacillus Paratyphosus and the Food- 

 Poisoning Bacilli. These bacilli are all microscopically indis- 

 tinguishable from the bacillus typhosus. They are Gram-negative, 

 motile bacilli, the flagella being sometimes few in number, and 

 they do not form spores. On ordinary media, growths have the 

 general character of those of the b. coli and b. typhosus, some 

 members in certain reactions resembling the one, and in others 

 resembling the other, but they do not ferment lactose. Opinion 

 differs as to their capacity to form indol, but usually the reaction 

 to this test is negative. 



The methods for the isolation of the members of the group 

 vary with the nature of the infected material to be examined. 

 In the case of abscesses caused by the bacillus paratyphosus, the 

 organism is usually accidentally discovered during the application 

 of ordinary methods. When deliberate search for a member of 

 the group is required, usually either the faeces or the blood con- 

 stitutes the material to be examined. In the former case, advan- 

 tage is taken of the fact that the food-poisoning bacilli do not 

 ferment lactose. Thus, if MacConkey bile-salt lactose-agar plates 

 (p. 50) be used, the organisms sought for will appear as colour- 



