228 ZOOLOGY 



the nucleus, which it is often difficult to make out on the 

 living animal. The whole substance of the Amceba is 

 mobile, so that the internal organs have no fixed relation 

 to one another. Quantities of Amoeba can usually be 

 obtained for study by gathering the mud from the edges 

 of stagnant pools, or by scraping the green growth from 

 flower-pots, and letting these gatherings, covered with a 

 little water, stand in a fairly warm place for two or three 

 weeks. 



Even the Protozoa bear important relations to man. 

 One species, Amceba coli, has long been known occasion- 

 ally to inhabit the food canal of man, and it is now known 

 that an amoebiform organism (probably one of the Sporo- 

 zoa) is the cause of malarial diseases. Since in one 

 common species 48 hours are required to complete a 

 developmental cycle, the recurrence of the fever every 

 alternate day is explained. It is now demonstrated that at 

 least one of the common agents in infection with malaria 

 is the mosquito, which carries the germs of the malaria 

 parasite from one host to another. Other Sporozoa, of at 

 least one species, are parasitic in the human liver, others 

 attack fish and cause them to die in large numbers; still 

 others cause sickness and death among domesticated 

 animals. The Texas fever among cattle is believed to be 

 caused by an organism 1 belonging to this group, the 

 inoculation of the cattle being effected by the cattle-tick. 



The reproductive capacity of Protozoa is so great that 

 their importance in the world, despite their small size, is 

 not astonishing. One of the early students of Protozoa, 

 Ehrenberg, computed that from one individual of Para- 

 mecium aurelia 268,000,000 might be developed in one 



1 Called Piroplasma bigeminnm. 



