THE INHERITANCE OF DISEASE 5O5 



There is also a great deal of evidence that the incidence 

 of spontaneous mahgnant tumors in animals is quite depend- 

 ent on the inheritance. 



DISEASES BASED ON ABNORMAL SENSITIZATION 



A number of disease conditions, all troublesome and some 

 very serious, asthma, hay fever, and various "idiosyncrasies" 

 against particular articles of food or particular drugs have 

 been found to have certain features in common. They are 

 ahke in that they are all unusual reactions to particular 

 substances found in the environment which do not affect 

 most people in any harmful way. Of those suffering from 

 the condition some react only to a single substance, others 

 are affected by many substances. The diseases are so common 

 as to be famihar to most people and place need not be 

 given here to any detailed description of them. The simplest, 

 and in many ways most characteristic, is uticaria, or hives. 

 Most people suffer at one time or another from this trouble. 

 Some people always have it as a consequence of eating a 

 particular food, e.g. strawberries, eggs. The skin becomes 

 blotched and irregular wheals are raised above the general 

 level of the skin surface by reason of the fact that the skin in 

 these areas is swollen. The swelHng is due to fluid in these 

 areas having left the blood vessels and stagnated in the tissue 

 spaces. In asthma the same general process occurs but 

 the area affected by the sweHing is the smaller air tubes 

 in the lungs and these are partly closed, making breathing 

 difficult. In hay fever it is the mucous membranes of the 

 eyes and nose which are affected. 



Inquiry has disclosed a well-marked famihal influence in 

 these conditions. They are in some measure inherited. The 

 inheritance seems to be based on recessive characters in the 

 Mendehan sense. There is a certain difficulty in this inter- 

 pretation, however, in that not all the offspring of matings 

 with both parents diseased are afflicted. This is susceptible 

 of alternative explanations. It may be that the inheritance is 

 dependent on multiple factors in which case the line between 

 dominant and recessive is not necessarily clean cut. Some 

 characters may be dominant, others recessive and the actual 

 behavior of the individual is the result of a kind of balance. 



