220 Changing Human Nature 



ing ages. The children of Itahans Uving in America are 

 taller than children of corresponding parts of the popula- 

 tion in Italy. Japanese children living in America are taller 

 than Japanese children living in Japan, and so on. In Eng- 

 land there was a marked decline of the average stature of 

 enlisted men toward the end of the last century. Both in 

 England and in Japan, measurements of enlisted men have 

 in recent years shown a tendency toward an increased stature. 

 In Japan, a study has just been completed of men enlisted 

 in 189 2- 1926 inclusive. During these 35 years there has 

 been an average increase of height amounting to i ^ inches. 



Physical and Physiological Differences 



Differences in physical traits tend to overlap differences 

 in physiological traits. It is sometimes impossible to dis- 

 tinguish the two. For example, we think of pigmentation 

 as a physical trait since it is apparent to the senses and can 

 be measured with a considerable degree of accuracy. The 

 formation of pigment, however, is the result of definite 

 chemical interactions and may quite properly be considered 

 a physiological character. Differences in voice, in suscepti- 

 bility to disease, in the rate of maturing, in the production of 

 milk, in the chemical character of the waste products, in 

 blood pressure, in capacity to digest various foods, are ex- 

 amples of physiological traits with regard to which individuals 

 of a given population are found to fluctuate. Recent studies 

 of the so-called blood types ^ show, on the one hand, that 

 each race has a distinct proportion of individuals of the va- 

 rious blood types, and on the other hand, that the blood types 

 are inherited, as are other physical traits. 



2 With improvements in the technique of blood transfusion has arisen 

 the difficulty that the blood of one person may not be compatible with the 

 blood of another. Extensive study of human blood primarily for the 

 medical purpose of determining the suitability of available blood for trans- 

 fusion in concrete situations has revealed the existence of " types " with 

 distinct modes of reaction. 



