xiii, b, 5 Haughivout: Flagellated and Ciliated Protozoa 241 



influenced by chemical changes originating in the cells and body 

 fluids of the hosts. 



The feeding habits of free-living forms may give a clue to 

 the working out of this problem. They have been extensively 

 studied by many workers, who have brought out important 

 points. Whether the reactions in these phenomena are purely 

 of a chemotactic nature or are combined with changes in surface 

 tension remains to be proved. The significant thing, however, 

 in connection with the theory I have just advanced is that these 

 reactions in the case of parasitic forms are not restricted to 

 the protozoa, but may be participated in by cells belonging to 

 the host. 



The most striking example of this that I can recall at' the 

 present time is that furnished by Lankesterella sp. This organ- 

 ism is parasitic in the nucleated erythrocytes of the frog. 

 Neresheimer 8 has described and figured the penetration of the 

 parasite into the erythrocyte. When the parasite and erythro- 

 cyte are separated by a distance about equal to the length of 

 the parasite, amoeboid movements on the part of the erythrocyte 

 become evident, and eventually the blood cell throws out two 

 long, pseudopodialike processes and, as Minchin remarks with 

 characteristic felicity, "opens its arms, as it were, to the para- 

 site, and engulfs it in a manner very similar to the ingestion of 

 food by circumvallation on the part of an amoeba." The para- 

 site is then drawn into the body of the erythrocyte, which rounds 

 out and resumes its normal form with the parasite in its interior. 

 In this instance it must seem that the parasite gives off some 

 substance that, even at a distance, awakens a reaction on the 

 part of the host cell, which brings about its own destruction by 

 aiding the entrance of the parasite. It is conceivable to me that 

 under certain conditions epithelial cells may do the same thing. 



The attraction of the gametes of protozoa is a process that 

 is possibly in line with the above and is sufficiently distinct from 

 anything shown by the bacteria to make us believe that in 

 dealing with the factors that determine the relations between 

 protozoan parasites and tissue cells we have something radically 

 different from the conditions that govern bacterial infections. 



Trichomonas flourishes only in an alkaline medium in the in- 

 testine. In the vagina it is found only in mucus having an acid 

 reaction and is quickly got rid of by douching with alkaline 



K Arch, f. Protistenk. (1909), 16, 187. 



