44 Report of the BilJiarzia Mission in Egypt, 1915 



activity of their tails or by creeping by means of their well-developed 

 suckers. AVhen actively swimming cercaria are poured from one 

 dish into another it is very noticeable that they immediately fix 

 themselves firmly by means of their ventral suckers to the surface 

 of the vessel into which they are carried until the motion of the 

 water has ceased, when swimming is again resumed. It seemed, 

 therefore, quite possible that if heavily infected water was drunk, 

 the cercaria, coming into momentary contact, might similarly 

 adhere to the mucous membrane of the mouth, tongue and oeso- 

 phagus and at once proceed to penetrate into the tissues. That 

 this actually can take place is apparently borne out by the follow- 

 ing experiment. Four sooty monkeys which had been taken, out 

 with the Mission in January and kept in separate cages in the 

 laboratory until the experiment was completed, were subjected to 

 infection with Bilharzia cercaria. In three cases the infected water 

 was poured into the bottom of the cages and the monkeys were 

 consequently exposed to infection through the skin of the hands, 

 feet, buttocks and tail. The fourth monkey was fed for a day or 

 two on dry food only, and then allowed to drink from a cup con- 

 taining filtered water swarming with Bilharzia cercaria. Some 

 effect, probably a prickly sensation, was produced almost imme- 

 diately, for the monkey began to pull down the lower lip, to rub 

 the mucous membrane of the mouth, and in other ways to indicate 

 that the drink had not been pleasurable. After a second experience 

 on the following day the monkey refused to accept water out of a 

 cup although thirsty. The four monkeys eventually died and all 

 showed a heavy infection with Bilharzia. The monkey infected 

 from drinking water showed earlier and much more intense 

 symptoms than the others. This experiment showed that in 

 Bilharzia infection may be both oral and cutaneous. As in ankylos- 

 tomiasis there is little doubt, however, that the infection enters 

 through the skin in the bulk of cases. 



As Brock [67] has pointed out, the chances of infection are much 

 greater in bathing than in drinking, because under the former 

 circumstances a much larger quantity of water comes into contact 

 with the body. 



Incubation Period of the Disease. 



The incubation period of Bilharzia has been variously estimated 

 by different writers. Sonsino gives from two to three years. 

 Sandwith considers that it ranges from three to six months. 



Hatch [222] in 1887 wrote : " The time between the contraction 



