CONTROL ()!• AMMAL PAJiASlTHS 255 



(clilori(l<' of lime), before they become scatterecl in sewage or 

 water or in the soil, or are earried, no one ran know where, 

 by liies, earthworms, or other livini.,^ agencies. This is an 

 effective method and can be delinitely workiMl into tlie habits 

 and sanitary regime of every liome, and will eventnally free 

 us from all (huio-erous infections; whereas tlie most intelli- 

 gent and conscientious of us cannot possibly kee[) our hands 

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

 sistently and always observe all the precautions necessary 

 to prevent infection if the oi'ganisms are scattered every- 

 where in soil, water, and food. 



Practical problems. The field is so vast and dillicult, 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. r>raun^ has 

 described nearly 400 animal [)arasites of man — ol protozoa, 

 40 liatworms, 43 threadworms, 39 ticks, and over 25(1 insects. 

 The mere fiofures nidicate how little we know al)out what is 

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

 edge marks little more than a l)eL!'innin<j:, and in addition to 

 liuman parasites other hundreds priw u[)on |)lants, and prob- 

 ably thousands upon otlicr animals, domesticattMl and wild. 

 We shall be able to suo'o-est but a few tvpes, and all the rest 

 may be studied alon<^ lines similar to those indicated. 



Parasitic protozoa. Alihough disi-overy of protozoan para- 

 sites in the blood of animals began with the studies of 

 Chaussat (185U) and l.ankesler (^1871), and several others 

 in the interim, it was the work of l.averan (1880) on tlie 

 1 Braun, The Aiiiiiuil Tanisites of Man. 1908. 



