MAN'S IMPROVEMENT OF HIS ENVIRONMENT 391 



be either natural or acquired. Natural immunity seems to be in 

 the constitution of a person, and may be inherited. Immunity 

 may be acquired by means of such treatment as the antitoxin 

 treatment for diphtheria. This treatment, as the name denotes, 

 is a method of neutralizing the poison (toxin) caused by the bacteria 

 in the system. It was discovered a few years ago by a German, 

 Von Behring, that the serum of the blood of an animal immune 

 to diphtheria is capable of neutralizing the poison produced by 

 the diphtheria-causing bacteria. Horses are rendered immune by 

 giving them the diphtheria toxin in gradually increasing doses. 



Antitoxin for diphtheria prepared by the New York Board of Health. 



The serum of the blood of these horses is then used to inoculate the 

 patient suffering from or exposed to diphtheria, and thus the dis- 

 ease is checked or prevented altogether by the antitoxin injected 

 into the blood. The laboratories of the board of health prepare 

 this antitoxin and supply it fresh for public use. 



It has been found from experience in hospitals that deaths from 

 diphtheria are largely preventable by early use of antitoxin. 

 When antitoxin was used on the first day of the disease no deaths 

 took place. If not used until the second day, 5 deaths occurred 

 in every hundred cases, on the third day 11 deaths, on the 4th 

 day 19 deaths, and on the 5th day 20 deaths out of every hun- 

 dred cases. It is therefore advisable, in a suspected case of 

 diphtheria, to have antitoxin used at once to prevent serious 

 results. 



Vaccination. — Smallpox was once the most feared disease in 

 this country ; 95 per cent of all people suffered from it. As late 



