306 GENERAL ZOOLOGY 



certain parasitic worms pass out in the urine and hatch 

 out larvae which bore through the skin; some diseases 

 (syphilis, gonorrhoea) are transmitted through the contact 

 of mucous membranes with those of infected persons and 

 are usually acquired by kissing or through sexual relations. 

 Small wonder, then, that with so many opportunities to 

 acquire diseases, measures are generally taken to combat 

 them. 



Modern medicine attacks disease along three general 

 lines. (1) Preventive medicine educates the public. It 

 spreads knowledge as to the nature of prevalent diseases 

 and tries to lessen chances for their dissemination by im- 

 proving sanitation, conditions of work, and diet. (2) 

 Corrective measures attempt to help the body to work 

 properly. Operative surgery adjusts structural defects; 

 physic retains water in the undigested food and stimulates 

 the flow of water into the intestine; strychnine in small 

 quantities sometimes serves as a tonic to a fagged-out 

 nervous system and allows it to recover its normal efficiency; 

 a change in diet may alleviate some specific irritation ; lenses 

 may correct defective vision. (3) The killing or preven- 

 tion of internal parasites is accomplished in various ways. 

 Quinine is effective in poisoning malarial parasites in the 

 blood corpuscles; thymol given judiciously will kill hook- 

 worms; the salts of mercury are injurious to the organisms 

 causing syphilis. The human body has within itself certain 

 reactions which are taken advantage of in preventing dis- 

 ease. Immunity to diseases may be natural or acquired. 

 Most persons will not grow the virus of infantile paralysis 

 in their bodies, thus showing a natural immunity. A person 

 who has been sick with smallpox will not contract the dis- 

 ease again; he has acquired immunity because his body has 

 formed antitoxins which prevent the growth of smallpox 

 organisms. Modern medicine has made it possible to 

 acquire immunity to certain diseases by contracting them 

 in a mild form through vaccination. Under such circum- 

 stances the body during light attacks of disease develops 



