BONE-BUILDERS 75 



call them drugs — which affect the working capacity of 

 both cartilage-builders and bone-builders. They can 

 incite them to work or send them to sleep. These sub- 

 stances or drugs are manufactured in small out-of-the- 

 way workshops called glands of internal secretion. One of 

 these lies within the skull, attached to the base of the 

 brain, and is known as the pituitary gland. In giants 

 this gland is always greatly and abnormally overgrown. 

 We have reasons for supposing that it has thrown a drug 

 or drugs into the blood which set all the bone-builders 

 into a state of frenzied activity, producing the dire disease 

 of growth called giantism. 



We have been speaking of the bone-builders as if they 

 were mere journeymen bricklayers. We have only to look 

 at the manner in which they have built the upper end of 

 the thigh-bone to see that they are highly accomplished 

 engineers (fig. 20). The upper end of the thigh-bone is 

 a bent lever ; for one instant in every step the weight of 

 the whole body rests on the ball-like head of the lever ; 

 the weight is transferred to the shaft of the bone through 

 the neck which rises upwards obliquely from the shaft. 

 The junction of the neck with the shaft is obscured by 

 two bony projections which serve as cranks for muscles 

 of the hip-joint, the greater and lesser trochanter (fig. 20). 



The construction of bent levers is a matter to which 

 engineers have had to give a great deal of attention, for it 

 is clear that if the bent part — represented by the neck of 

 the femur — is not rightly planned, it will be liable to snap 

 under an undue weight. The construction of the neck 

 of the upper end of the thigh-bone can be studied in the 

 living bone as well as in the dead one. Fig. 20 represents 

 a picture of it taken by X-rays. We see that the bone- 

 builders or osteoblasts have laid down and fixed their 

 struts and ties in a very elaborate and ingenious manner. 

 From the inner wall of the hollow cylindrical shaft 

 (fig. 20) issues a great spray of fine plates or beams of 

 bone which ascend to end in the head, shaped like a half- 

 ball ; they serve as struts, and receive the chief pressures 

 or weights falling on the head of the thigh-bone. Then 



