146 FAMILY STUDIES IN BUILD. 



genitalia appear under-developed— infantile. The obesity frequently 

 affects the region of the pelvis only or chiefly, though the thighs also 

 may be involved. Disfunctioning of the pituitary in later years is 

 believed, likewise, to induce obesity. Of this disfunctioning there are, 

 doubtless, all degrees corresponding to the variety of grades of obesity. 

 Thus a second factor of obesity must be recognized; and this also 

 "runs in families" — is hereditary. 



The other endocrine factors in obesity are less precisely known. It 

 is believed that the interstitial cells of the gonads secrete hormones 

 that regulate, especially inhibit, the production of fat. This is inferred 

 by the frequent tendency of women after the menopause to grow fat 

 and of eunuchs (of one type, at any rate) to become fleshy. Also, the 

 secretions of the islands of Langerhans of the pancreas are known 

 to influence carbohydrate metabolism, so that when they do not 

 function properly sugar is eliminated unchanged in the urine, and 

 "diabetes," usually accompanied by fleshiness in its early stages, 

 ensues. Of course, it can not be stated that pancreatic insufficiency 

 is responsible for the prediabetic obesity ; but the relation of the two 

 phenomena is undeniably close. 



Thus there come clearly to view two links in the chain of causes 

 connecting chromosomal factors (such as are present in "Mendelian" 

 heredity), on the one hand, and build, on the other. First, two or 

 more of the endocrine glands play a great role in metabolism and 

 when disturbed usually result in an abnormal build; and, secondly, 

 just the condition of endocrine disfunctioning is an hereditary one 

 and seems to depend on the condition of the enzymes or catalyzers 

 that must be in the chromosomes. 



That other constitutional conditions than those of the larger endo- 

 crine glands may play an important role in metabolism can not be 

 denied; probably the quality of the protoplasm of every active cell 

 influences the bodily metabolism; but the endocrine glands proper 

 seem, as it were, to be told off for this specific purpose, and thus 

 peculiarities in their functioning lead to striking results. 



Evidence of Segregation in the Heredity of Build. 



The best single criterion of Mendelism in any hereditary distribu- 

 tion is segregation. If there is sufficient evidence of segregation in 

 our study of build, then we are justified in concluding that build is 

 inherited in "Mendelian fashion." There have been several occasions 

 to refer to evidence of segregation in this work; some of this evidence 

 may be brought together here and other added. 



1. The difference in variability of the progeny of different matings. 

 The offspring of slender parents are least variable, of fleshy parents 

 most. This is evidence that the fleshy parents carry gametes for 



