66 HUMAN PHYSIOLOGY 



of inflammation really represent the signs of con- 

 flict which is being waged in the bodily domain. If 

 the white corpuscles be defeated and the inflammation, 

 instead of being allayed and subsiding, proceeds to 

 the length of suppuration, (that is the formation of 

 pus or matter), we discover that " matter " really 

 consists of the dead bodies of the defeated white cor- 

 puscles. As such it may constitute, like the soldiers 

 left dead on a battlefield, a source of danger to the 

 territory around, and may set up disease in other 

 parts of the body. Such is the history of the white 

 blood corpuscles which practically in all animals thus 

 appear to discharge the duty of a sanitary force, ever 

 on the alert to combat invasion of the body by disease- 

 producing particles. 



THE HEART. By a somewhat circuitous route we 

 have at last returned to the central system of the cir- 

 culation, the heart itself. Any heart, from that of the 

 insect to that of man, may be described as a hollow 

 muscle. It is hollow to receive blood, and it is mus- 

 cular that it may contract to expel that fluid in the 

 proper directions. There is thus no mystery about 

 the heart and its action. The same form of energy 

 by which we move our fingers, arms, or legs, repre- 

 sents the force which circulates the nutrient fluid 

 through our frame. A glance at the heart of a bul- 

 lock in a butcher's shop will at once show us that its 

 substance is similar to the animal's flesh. Both are 

 composed of muscle with this difference that the 

 heart is composed of involuntary muscle fibres, that 

 is, it acts independently of the will, whereas the or- 

 dinary muscles of arms, legs and so forth, are termed 

 voluntary because they can be brought into action 

 when we desire movements to be performed. At the 

 same time, the heart can be affected, as will be seen, 



