i6o HUMAN BONE 



as the work done by the left ventricle at each 

 systole; and adding to this the work done by 

 the right ventricle (about a third that of the 

 left) we have 2J + f = 3 foot-pounds as the 

 work done by the heart at each contraction.' * 



In the illustration we see only an exceed- 

 ingly small portion of the muscular structure 

 of this most wonderful organ (Fig. 48). Its 

 fibres are visible ; they are columnar and faintly 

 striated; the nuclei are distinctly seen. Each 

 fibre is branched, and there is no covering. 



The original photo-micrograph shows an 

 amplification of 550 diameters: the time of 

 exposure to gaslight was 5 minutes ; the focal 

 distance was 72 inches; and the objective 

 used was the J-inch ; the eye-piece of 5 

 diameters was also used. 



Human Bone. 



Speaking generally, bone seems to have three 

 distinct duties it gives support and firmness 



* Kirkes, Handbook of Physiology. Morrant Baker's 

 Edition. (John Murray.) 



