PATHOGENIC BACTERIA AND DISEASES 49 



Next to water, milk is the most frequent carrier of the 

 infective germ. Raw oysters and uncooked vegetables 

 may convey the infection. The pernicious practice of 

 fattening oysters on sewage has been the cause of untold 

 deaths of typhoid fever in the past. Flies frequently 

 carry the infection from out-houses to foods of various 

 kinds. The site of infection is the Peyer's patches of 

 the small intestine, though the germ is found in the blood, 

 milk, spleen, liver, and lymphatic glands, and it is 

 thought it may gain entrance through the tonsils. 

 Locally, there may be ulceration of the intestines, which 

 ofttimes leads to hemorrhage and even perforation. 

 The symptoms of the disease are those of a continued 

 toxemia, fever, exhaustion, and delirium. 



Typhoid Carriers. Cultures of bacteria may remain in 

 the gall-bladder or other organs for months or even years, 

 the individual suffering no inconvenience, and thus 

 becoming a walking source of infection for others. 



Widal Test. When the blood of a person suffering 

 from typhoid fever is mixed with a living culture of 

 typhoid bacteria and examined in the hanging drop with 

 the microscope, the bacteria are seen to clump together 

 and cease their movements. This is due to the agglutin- 

 ating property of the blood in this infection, spoken of 

 elsewhere. 



Drying of the blood and considerable dilution does not 

 interfere with its accuracy, so that in practice a drop of 



blood is drawn on to a piece of filter-paper and sent to 



4 "' 



