116 INTESTINAL FLAGELLATES AND CILIATES 



withstand the action of the acid juices of the stomach. None of 

 the human intestinal Protozoa require a second host to transmit 

 them as do the blood-dwelling parasites. While outside the 

 body they remain dormant in their cysts for weeks or months 

 until they can gain access to a host again through food or water. 

 There is still much doubt as to the extent to which intestinal 

 protozoans are confined to particular hosts. Some workers 

 believe that each animal has its 'own species peculiar to it, and 

 that these species are not capable of infecting different hosts. 

 Evidence is accumulating, however, to show that in some cases 

 at least this is not so, and that many intestinal protozoans of 

 man are able to live in such animals as rats, mice and hogs. 

 Most intestinal protozoans are of very wide geographic distri- 

 bution, their abundance in any given place being largely deter- 

 mined by the warmth of the climate and the sanitary, or rather 

 unsanitary, conditions. 



As remarked before there has been much discussion concerning 

 the effect produced by various species of flagellates in the in- 

 testine. Naturally these parasites are seldom discovered except 

 when there is some intestinal ailment, since in normal health 

 faeces are seldom submitted for examination. Where routine 

 examinations have been made regardless of physical condition, 

 it has been found that a large per cent of people in unsanitary 

 places are infected. Stiles, in a town in one of our southern 

 states, found that from 50 to 100 per cent of the children were 

 infected, and it would probably be easily within the bounds of 

 truth to say that 75 per cent of all people in warm countries liv- 

 ing in places where unsanitary conditions prevail are subject 

 to infection with one or several species of intestinal Protozoa. 

 As Stiles has pointed out, such infection usually means that the 

 infected person has swallowed human excrement, since it would be 

 impossible for any natural agency to separate the microscopic 

 protozoan cysts from the faeces in which they are found. This 

 fact, impressed upon the mothers of infected children, especially 

 when accompanied by the remark that one could not tell whether 

 the infection had come from the excrement of a white or a negro, 

 was found by Stiles to be one of the most powerful means of 

 improving sanitary conditions in the South. 



Facts which support the view that intestinal flagellates are of 

 more importance pathogenically than has commonly been sup- 



