CONTROL OF THE ENVIRONMENT 



FOR HEALTH 



CHAPTER XXIX 



HOW DISEASES ARE CAUSED 



Questions. 1. Can anything in food make people sick? 2. Can any- 

 thing in the air or water make people sick ? 3. Can the lack of anything 

 in food, air, or water make people sick ? 4. Can things get into the body 

 in other ways than through the food, air, and water, and make people 

 sick ? 5. In what ways can living things be injurious to other species of 

 organisms ? 6. How can injuries to organisms be remedied ? How can 

 they be prevented ? 7. Why must there be sickness ? 



231. The food relation between organisms. We know now 



( I ) that every living thing must have food ; ( 2 ) that chlorophyl- 

 bearing organisms are the only ones that can manufacture food 

 out of inorganic raw material ; and (3) that all other organisms 

 must supply their needs from the bodies of such food producers. 

 These dependent species, in many cases, get their food from the 

 bodies of plants and animals that are already dead. Thus, 

 molds (fungi) of many kinds are found on dead plants and ani- 

 mals, as well as on organic materials artificially worked up — 

 bread, cheese, leather, and so on. Other species of fungi are 

 mildews and mushrooms ; the former are found growing on 

 cloth, the latter on cut timber or railroad ties. Many insects 

 and worms live upon all sorts of dead organic matter, from the 

 carrion beetle and clothes moth to the common earthworm. Then 

 there are the myriads of protozoa and bacteria living in the soil 

 and in all natural waters, using dead organic material as food. 

 Most of the familiar animals and a number of plants attack 



living things and destroy them for their own food. The gentle 



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