INHERITANCE OF ALLERGY 317 



allergy to manifest itself. The reason for this is that with the normal varied 

 diet which most adults enjoy, there is little chance that a person can escape 

 the sensitizing protein long after reaching adulthood. 



That both a definite heredity and a definite environment are necessary 

 to produce a given character is well known and many cases of both animals 

 and plants might be cited to support this principle. 



An interesting fact early observed in this study was that allergic persons 

 commonly marry into allergic families. This is still true even in the cases 

 where one or both of the individuals concerned are themselves negative. 

 Our records include only a few cases in which marriage occurs between a 

 person from an allergic family and one from a negative line. The explana- 

 tion for this fact can only be conjectured. Allergic families have been 

 found to be usually of a high grade of intelligence, and as Balyeat (1929) 

 has shown, a hay fever sufferer customarily has a higher IQ than does the 

 average person. It may be surmised that this fact has something to do 

 with the frequent marriages between allergic families and that in some cases 

 their higher intelligence serves as a mutual attraction. Since allergic 

 persons make up only a small percentage of the entire population, their 

 frequent marriage is worthy of note, although no means is at present known 

 which favors the mating of these persons. 



In our paper on hay fever we have stated that some families show only 

 one form of allergy. It is seldom, however, that any family is specific for 

 one allergy alone. Only one of the twelve families of our earlier paper 

 showed no allergy but hay fever. One had only asthma and hay fever, 

 and the other ten had in addition either eczema, bronchitis, urticaria, mi- 

 graine, or a combination of several of these allergies. 



Our present study of forty-one families shows similar conditions. Only 

 five (families no. 22, 23, 27, 37, and 40), exhibit branches which before 

 crossing with other allergic families, show nothing but migraine, and in 

 most of the families there are various combinations of the different allergies, 

 a single individual sometimes suffering from four to five types. (Example, 

 family 8.) In eleven families there are two kinds of allergy and in twenty- 

 six there are three or more. 



Since in the families from whom we have collected data, so many forms 

 of allergy are present, and since allergies commonly marry individuals from 

 similar families, it is extremely difficult to determine positively the number 

 of genetic factors that cause the different forms of sensitivity. 



In our present study we have endeavored to ascertain whether our pedi- 

 grees could be explained as due to the operation of several genes acting 

 together, perhaps one gene being necessary for an individual to become 



