498 ■ HUMAN BIOLOGY 



Statement of the number of factors involved and an indica- 

 tion of the way they may exert their effects. 



In the guinea pig it is found that there are inherited 

 factors which influence the quantity of antibodies (antitoxic 

 substances) which are produced in response to a given 

 stimulus. There are other inherited factors which influence 

 the severity and precise quahty of the ulceration which the 

 tubercle bacillus and some other irritating agents produce 

 in the skin, and in the character of the tuberculous inflamma- 

 tion in the lymphatic vessels and glands. There is aIso]^an 

 indication of another group of separately inherited factors 

 affecting the nature of the reaction to dietary deficiencies. 



Granted that there are inheritable factors influencing the 

 character of tuberculosis in the individual, any clue as to 

 their dominant or recessive quality is a matter of great 

 interest. Unfortunately the human material lacks the 

 precision of detail necessary for an answer to such a question. 

 The guinea-pig material suggests that where all of the 

 characters favorable to resistance are combined in a family 

 it presents a dominant combination. The first generation 

 crossbreds are as resistant as the most resistant family. In 

 the actual observations they somewhat surpass this mark, 

 indicating the operation of those forces which make for 

 heterosis or hybrid vigor. Where crosses are made between 

 families of less than the maximum resistance the result 

 varies. Some crosses produce offspring as resistant as the 

 better family, another produces an intermediate resistance. 

 In general, dominance of resistance prevails but it is 

 imperfect. 



The available information from all sources with respect to 

 the inheritance of a variable degree of resistance to tubercu- 

 losis suggests some further comment in relation alike to 

 its medical aspects and to the genetic point of view. 



Belonging essentially to the prebacterlologlcal era of 

 pathology Is the conception that susceptibility to infectious 

 disease is more or less definitely related to fundamental 

 Inheritable qualities which find expression In physical 

 conformation, that is, "physical type," and in peculiarities 

 of function, that is "'Constitution." The terminology was on 

 the whole very loose and Interchangeably employed. Con- 



