346 BIOLOGY AND HUMAN LIFE 



Dr. Bela Schick, an Austrian physician, works on a some- 

 what similar principle. The Schick test has been applied to 

 half a million children in New York City alone, and those 

 who appeared susceptible were treated with the toxin-antitoxin 

 mixture, making them immune. In this way many cases of 

 diphtheria are prevented, and it is reasonable to hope that in 

 time this disease will be as rare in civilized communities as is 

 smallpox or plague.^ 



263. Disease and heredity. In a given family many mem- 

 bers may have suffered from the same disease, as tuberculosis. 

 We know now that tuberculosis and other diseases are not in- 

 herited in the same sense as the color of the eyes or the shape of 

 the thumb is inherited. Where tuberculosis runs in a family, 

 two facts are to be distinguished : 



1. If one member of a family has the disease, the other mem- 

 bers are more likely to be exposed to injection than they would 

 be otherwise, and so the disease spreads in that family. 



2. Where a person has tuberculosis (or any other disease), 

 the indications are that this person has not a natural immunity 

 to the disease ; in other words, he is susceptible to it, or has a 

 disposition toward it. Now it is this natural susceptibility (or 

 immunity) which is inherited, and not the disease. No matter 

 how much susceptibility one had to a given disease, he would 

 not contract that disease unless he was exposed to injection by 

 the specijic microbes that cause that disease. This point is 

 tragically demonstrated by the rapid dying out of the inhabit- 

 ants of certain of the South Sea Islands. The natives of these 

 islands appeared to be extremely susceptible to measles and 

 tuberculosis, as well as to various other diseases that are com- 

 mon in Europe and America. The natives had never experienced 

 these diseases, however, until the foreigners brought the germs 

 to them. Then the natives died out very rapidly. 



1 Experiments have been carried on in Chicago by Drs. George and Gladys 

 Dick, to find a susceptibility test for scarlet fever. This Dick test has been 

 tried out by physicians in several cities and promises to be a useful aid in pre- 

 venting sickness. 



