DISTRIBUTION OF DISEASE GEKMS 97 



Do you think these laws are just ? Do you know of cases 

 where the laws have been broken ? Was it justifiable to 

 break quarantine ? Is it in any sense indecent or unclean 

 for one to have typhoid ? 



109. Mosquitoes and malaria. There is a strong popular 

 antipathy to mosquitoes. In themselves they are merely an 

 annoyance, but because of disease germs that may sometimes 

 live in the bodies of certain kinds of mosquitoes, and which 

 may be transferred to the bodies of men, they may become a 

 positive danger. In order that we may understand the relation 

 between mosquitoes and malaria, and know how to prevent 

 malaria, we must discuss both the disease and the mosquito. 



110. Malaria caused by an animal organism. When a per- 

 son has malaria, his red blood corpuscles are more or less 

 infected with an extremely small one-celled animal. One of 

 these malarial organisms lives within a red blood corpuscle 

 for a brief period (three days in case of one kind of malaria), 

 and by the end of that time has undergone repeated divisions, 

 resulting in the formation of several of the organisms. The 

 wall of the blood corpuscle breaks, and all the newly formed 

 malarial parasites are set free in the liquid of the blood. It is 

 usually just after many such parasites are set free in the blood 

 that the paroxysm known as the malarial chill ensues. The 

 germs may enter other red blood corpuscles, and in due time 

 another crop of their kind will have been produced and another 

 chill ensues. We must discuss the life history of the mosquito 

 before continuing the discussion of malaria. 



111. The life history of the mosquito. Mosquito eggs are 

 laid in little groups on the surface of the water (fig. 53, A). 

 When the eggs hatch, the individual emerging from each egg 

 is a little squirming, insect-like creature, technically called a 

 larva but popularly known as a " wriggler " (fig. 53, (7). The 

 eggs may hatch in less than a day after they are laid. The 

 larvae live about seven days in warm weather, but longer if 

 the temperature is cool or if the food for the larvae is scarce, 



