MODE OF INFECTION. 263 



I may premise that Balantidium is by no means so sensitive to 

 the influences of water and cold as the intestinal Monads. Even 

 after copious application of water, we can, without using a warm 

 stage, see the Infusorians moving for a long time without apparent 

 diminution of vigour. But later the animals become wearied, they 

 remain lying on the object glass, and finally suspend the play of 

 their cilia. But even in this state they retain unchanged for hours 

 a fresh appearance. One does indeed find some specimens which 

 are already more or less strongly contracted, and have lost all their 

 covering of cilia, except a few adoral ones. The granular interior 

 mass has gathered together into a heap, from which some large drops of 

 fat shine out. Later still, the cilia and the epistome have disappeared, 

 and the body finally appears as a ball (0*08 to O'l mm.), which is 

 surrounded on all sides by a capsule-like thickened cuticle, but still 

 encloses as before a clearer peripheral layer and a dark central mass 

 with fat-drops. The origin of the -cyst admits of no doubt, for one 

 can often observe in its earlier stages the nucleus and the vacuoles of 

 Balantidium. Since this capsule is found in the deposited and even 

 somewhat dry excrement, one may perhaps conclude that its forma- 

 tion as above described is an entirely normal process, occurring perhaps 

 in all, and at least in many of the parasites expelled with the excre- 

 ment. That the Balantidium-c&psulQ plays an important part in the 

 preservation and transference of these animals, is not only in itself 

 most probable, but finds justification and confirmation in the facts 

 known regarding Opalina. One may indeed doubt whether it is these 

 encysted Balantidia exclusively which bring about the infection, or 

 whether the newly voided animals are not sometimes directly trans- 

 ferred to the intestine, there again to become its denizens. So far as 

 man is concerned, this question is indeed irrelevant, seeing it could 

 hardly happen that he thus infected himself. But it is quite the 

 reverse with swine, which, with their dung-eating habits, might easily 

 afford opportunity for such a mode of infection. 



In support of the position that an effective transmission is only 

 brought about by means of the encysted animals, I lay but little 

 emphasis on the fact that the attempts of Ekeckrantz and Wising to 

 infect dogs and other mammals ( per os et per anum) with dung con- 

 taining Balantidium, have all yielded only a negative result ; but I rely 

 rather on the well-known fact that small delicate skinned Entozoa, as 

 these forms undoubtedly are, cannot without a protective covering 

 survive in the stomach of an animal (p. 76). And it is through the 



thinks that one must not transfer the results of the observation of the Balantidium in 

 swine to that found in man, and sees in this a further reason for not regarding man as the 

 proper and natural host of this parasite. 



