?8 PRACTICAL ZOOLOGY 



known and so important that the house fly is now often spoken 

 of as the typhoid fly. 



Typhoid Fever. - - The typhoid fever germ is a bacillus (Bacil- 

 lus typhosus) about T oi<nr of an inch long (Fig. 48, A). It 

 occurs principally in the intestine, lungs, blood, and bladder of 

 man, and is taken into the alimentary canal with water, ice, 

 milk, and other foods. Typhoid bacilli are discharged from the 

 body in the excretory matter and in sputum. It is therefore 

 very important that all excretory matter from typhoid fever 

 patients be screened from flies or treated so as to kill the germs. 

 In certain cases the patient may have, to all appearances, com- 

 pletely recovered and yet continue excreting the typhoid bacilli. 

 These cases are known as " carriers " and the number of such 

 " carrier " cases who continue to carry the typhoid germs in their 

 bodies is gradually increasing as the matter is being more care- 

 fully investigated. It is being discovered that many of the 

 inexplicable outbreaks of typhoid fever are due to the presence 

 of one of the chronic carriers. The presence of an unrecognized 

 " carrier " excreting infected matter, the occurrence of large 

 numbers of flies, and their access to food or milk are all the 

 factors that are required to initiate an epidemic of typhoid 

 fever, and not a few epidemics are now being traced to the con- 

 currence of these factors. 1 



Dysentery. - - Similar in some respects to the typhoid bacillus 

 is the bacterium that causes summer diarrhoea or dysentery in 

 children. The germ (Bacillus dy sentence) resembles that of 

 typhoid in size and shape, and is taken into the system with 

 water and foods in the same way. The bacilli are especially 

 active in the intestines, where they cause serious disturbances, 

 often resulting fatally. It has been shown quite clearly that the 

 number of cases of summer diarrhoea corresponds very closely 

 to the number and activity of house flies. During wet seasons, 

 which are unfavorable for the multiplication of flies, the number 

 of cases of dysentery is much smaller than during dry seasons. 



1 Uewitt. C. G., House-Flies and how they spread Disease. 



