50 THE HUMAN BODY 



that a peculiar disease, acromegaly, in which there is abnormal en- 

 largement of some of the bones, notably of the face and extrem- 

 ities, is associated with overgrowth of a mass of tissue at the base 

 of the brain. This tissue mass, the pituitary body (Fig. 60), is 

 formed in part by an outgrowth downward from the brain, and in 

 part by an outgrowth upward from the roof of the mouth. The 

 latter portion, known separately as the hypophysis, appears to be 

 particularly concerned with bony growth. The theory of this 

 control which best explains the known facts is that a hormone is 

 secreted and poured out into the blood which by its presence 

 stimulates growth of the bones. The more abundant the hormone 

 the more vigorous is the growth. The enlargement of the hypoph- 

 ysis which occurs in acromegaly would account for the occurrence 

 of a more abundant secretion of the hormone. A similar enlarge- 

 ment appears to characterize the condition of gigantism, which 

 gives rise to the giants exhibited in side shows. Although there 

 is no positive proof, it seems reasonable to suppose that the oppo- 

 site condition, dwarfishness, is a result of a deficiency of the pitui- 

 tary hormone. 



We need to bear in mind in discussing hormone action that when 

 an effect is attributed to a hormone we have not offered a complete 

 explanation of it, but only moved the explanation a step farther 

 along. We can say that a man's height is determined by the 

 activity of his pituitary body, but we are still in the dark as to the 

 factors that regulate the latter. Particularly are we ignorant of 

 the manner in which secretion of the hormone is modified when the 

 man has "gotten his growth." 



Another body, the thyroid, located at the front of the neck, is 

 believed to secrete a hormone which regulates the development of 

 connective tissue. This function of the thyroid is, however, sub- 

 ordinate to its major function, which is concerned with the nervous 

 system. Detailed discussion of the thyroid is deferred, therefore, 

 to that connection, 



Hygienic Remarks. Since in the new-born infant many parts 

 which will ultimately become bone consist only of cartilage, the 

 young child requires food which shall contain a large proportion of 

 the lime-salts which are used in building up bone. Nature provides 

 this in the milk, which is rich in such salts (see Chap. XXXIV), 

 and no other food can thoroughly replace it. Long after infancy 



