306 SOME MINUTE ANIMAL PARASITES 



may suffer from protozoal parasites in some part of 

 the world. Fortunately, in many cases, the loss can 

 be controlled to some extent by precautions exercised 

 against the transmitters of the disease. 



Animal parasites affect man in another direction. 

 Were it not for the big game that act as reservoirs 

 of Trypanosoma gambiense and T. rhodesiense, without 

 themselves being harmed, the prevalence of sleeping 

 sickness in man probably would be reduced. Balan- 

 tidium coli from pigs is spread to man by the cysts 

 that pollute food or drink. These cases are clear, 

 but not so numerous as are the examples of parasitic 

 worms that spend one part of their lives in domestic 

 animals, especially cats and dogs, and the remainder 

 in human beings. 



The study of parasitic Protozoa in relation to the 

 food-supply of nations is, then, of the utmost economic 

 importance. The work is both tedious and expen- 

 sive, and in England there are not the opportunities 

 for such investigations as are afforded in America. 

 There, a great State Department the Bureau of 

 Animal Industry devotes the whole of its attention 

 to the study of the people's food-supply, the suppres- 

 sion and cure of animal diseases, and the improve- 

 ment of the methods of production of stock. 



The transport problem, again, brings to the fore 

 the importance of the study of the parasitic Protozoa. 

 Cattle are used for transport as well as food. Horses, 

 mules, and camels, are constantly employed for the 

 conveyance of goods where railways are distant or 

 inconvenient, and waterways not available. Agri- 

 cultural operations in many districts, it is true, are 



