OUR SMALLEST LIVING THINGS 



219 



to scarlet fever is developed by use of small quanti- 

 ties of the scarlet fever toxin alone. 



How do bacteria enter the human body? Bacteria 

 may enter the body through the digestive tract. They 

 may be in the food we eat. Typhoid fever and tuber- 

 culosis bacteria are sometimes taken in with milk or 

 water. Drinking cups, pencils, toys, our hands, and 

 other objects may have germs on them and infect 

 us if we put them into the mouth. Common colds, 

 diphtheria, and scarlet fever are known to be spread 

 in this way. 



FIG. 347. SNEEZING THE WRONG WAY AND THE RIGHT WAY 



Another common avenue of invasion for bacteria is 

 through the nose. Droplets of sputum are thrown into 

 the air when people sneeze and cough, and these are 

 breathed in by other persons who may be near. Bac- 

 teria that produce colds, pneumonia, and diphtheria 

 often enter the body in this way. A handkerchief 

 should always be held over the nose and mouth while 

 one is coughing or sneezing. 



Certain germs enter the body through breaks in 

 the skin. Cuts and scratches serve as an entrance for 

 bacteria. Germs of tetanus (commonly called lock- 

 jaw) enter the body by this avenue. Certain in- 

 sects puncture the skin of the body and thus in- 

 troduce germs. The germs of malaria, yellow fever, 

 and African sleeping sickness are transmitted in this 

 manner; however, the germs that produce these dis- 

 eases are not bacteria but are tiny one-celled animals. 



What can an individual do to help his body resist 

 disease? All diseases that spread in a community are 

 caused by germs. Every person who has a contagious 

 disease must have received the germs from someone 

 else who had the disease or from some animal that 

 was infected. A person need not always come in direct 

 contact with a patient, for a number of contagious 

 diseases may be spread through air, food, or water. 

 Contagious diseases would probably disappear en- 

 tirely if people who have them were careful not to 

 spread them. 



There are a number of ways in which every per- 

 son can help control diseases. The appearance of 

 such epidemic diseases as influenza, smallpox, diph- 

 theria, infantile paralysis, and scarlet fever should be 

 reported immediately to the Health Department. The 

 house of the patient will be quarantined by the health 

 officer, who places a card on the front of the house, 

 warning people not to enter. In some communities 

 people afflicted with dangerous contagious diseases 

 are kept separate in special hospitals provided for 

 this purpose. 



Everything about a sick person should be carefully 

 disinfected. Clothing and dishes taken from the sick 

 room should be immediately treated with substances 

 that will kill germs. All discharges from the patient 

 should be properly disinfected. Various chemicals 

 such as bichloride of mercury, carbolic acid, and 

 chlorinated lime, all powerful disinfecting agents, are 

 available for this purpose. 



Sometimes powerful gases are generated in a sick 

 room at the end of the illness. Formaldehyde and sul- 

 phur dioxide are the chemicals most commonly used. 

 This process is called fumigation. Fumigation is not 

 now considered important and is seldom used except 

 to destroy insects. 



If epidemics of smallpox or typhoid fever occur, 

 every person in the community should be vaccinated. 

 It is important to remember that vaccination does 

 not produce immunity for life. In the case of small- 

 pox vaccination, immunity lasts for about seven years. 

 If you were vaccinated when you were six years old 

 and you are now fourteen years old, you probably 

 are no longer immune to smallpox germs. Therefore 

 you should be vaccinated again. A large number of 

 states require vaccination of all children before they 

 enter school, but very few, if any, require vaccination 

 more than once. In view of the fact that vaccination 

 does not give immunity for life, do you think that 

 states should require vaccination of its citizens more 

 than once during a lifetime? Perhaps you can arrange 

 to debate this question in your general science class. 



With the introduction of the microscope as a 

 tool of science came the discovery of the world of 

 tiny plants and animals. Anton van Leeuwenhoek 

 (la'ven-hook), a Dutch clothing merchant, who 

 ground lenses as a hobby, was the first to devote 

 much time to the study of living things with a mi- 

 croscope. He made and perfected his own instruments. 



In 1683, Leeuwenhoek announced his discovery of 

 bacteria, and from the sketches and descriptions he 

 made of them, we believe that he saw all three forms 

 round, rod-shaped, and spiral. Almost two hun- 

 dred years elapsed, however, before the connection 

 between bacteria and diseases was suspected. It re- 

 mained for Louis Pasteur, a French scientist, about 

 1860, and later Robert Koch, a German experimenter, 



