MICROORGANISMS AND HUMAN WELFARE 41 



Since the introduction of compulsory vaccination, smallpox is be- 

 coming very rare. 



38. Hydrophobia and the Pasteur treatment. Hydrophobia, or 

 rabies, is a disease due to the bite of a mad dog, cat, or wolf. Until 

 the latter part of the nineteenth century the only known method of 

 treating this disease was that of burning out or cauterizing the 

 wounds with hot irons or nitric acid. After a long series of investi- 

 gations, however, Louis Pasteur (Frontispiece), a French scientist, 

 made known to the world the so-called Pasteur treatment (1885). 

 Pasteur found that the disease was located in the spinal cord, and 

 that, if pieces of the spinal cord of a rabbit which had died of hy- 

 drophobia are allowed to dry in the air, the germs gradually lost 

 their virulence. He therefore began the treatment of patients who 

 had been bitten by mad dogs by first injecting beneath the skin an 

 emulsion made from the spinal cords which had been dried for four- 

 teen days. Each day for twenty-one days an injection was made 

 from a cord that had been dried for a shorter time. Since hydro- 

 phobia usually does not develop in human beings for two weeks to 

 four months after the bite of a mad dog, the cells of the body by 

 this Pasteur treatment gradually acquire the power to resist the 

 hydrophobia toxins, and so the disease is prevented, if the wound 

 is cauterized at once and treatment begun immediately. The cau- 

 terization is of value even after a delay of twenty-four hours. 1 



39. The cause and prevention of other diseases. The 



germs that cause scarlet fever, yellow fever, measles, whoop- 

 ing cough, and infantile paralysis have not as yet been dis- 

 covered. Since, however, they are all infectious diseases like 

 tuberculosis and diphtheria, they must be due to some form 

 of microbe. Those in yellow fever, measles, and infantile 

 paralysis are so small that they pass through stone filters, 



1 The authors are much indebted to Dr. W. H. Park, Director of 

 the Laboratory of the Board of Health of New York City, for his 

 suggestive criticism of the sections relating to disease-producing bac- 

 teria. 



