CONTROL OF ANIMAL PARASITES 255 



(chloride of lime), before they become scattered in sewage or 

 water or in the soil, or are carried, no one can know where, 

 by flies, earthworms, or other living agencies. This is an 

 effective method and can be definitely worked into the habits 

 and sanitary regime of every home, and will eventually free 

 us from all dangerous infections ; whereas the most intelli- 

 gent and conscientious of us cannot possibly keep our hands 

 clean enough, boil or filter all our drinking water, or con- 

 sistently and always observe all the precautions necessary 

 to prevent infection if the organisms are scattered every- 

 where in soil, water, and food. 



Practical problems. The field is so vast and difficult, and 

 knowledge is growing so fast, that the only course for the 

 student to follow is to make connection with the best sources 

 of information, local boards of health and the scientific de- 

 partments of each state and of Washington, so as to keep 

 abreast of important discoveries. In this way all will be able 

 to help themselves and one another. Apply the quiz at the 

 beginning of this chapter to all the parasitic diseases of 

 plants, animals, or man of local importance. Braun 1 has 

 described nearly 400 animal parasites of man 31 protozoa, 

 40 flatworms, 43 threadworms, 39 ticks, and over 250 insects. 

 The mere figures indicate how little we know about what is 

 literally "eating" us most of the time. Our present knowl- 

 edge marks little more than a beginning, and in addition to 

 human parasites other hundreds prey upon plants, and prob- 

 ably thousands upon other animals, domesticated and wild. 

 We shall be able to suggest but a few types, and all the rest 

 may be studied along lines similar to those indicated. 



Parasitic protozoa. Although discovery of protozoan para- 

 sites in the blood of animals began with the studies of 

 Ohaussat (1850) and Lankester (1871), and several others 

 in the interim, it was the work of Laveran (1880) on the 

 1 Braun, The Animal Parasites of Man. 1908. 



