6 THE MECHANISM OF LIFE 



of beat increases. Other muscles of the chest and abdomen, 

 which before were inactive, now become employed to increase 

 the capacity of the thorax, and so to draw more air into the 

 lungs. The shoulders and arms are used as the air becomes 

 more and more deficient in oxygen and richer in COg, and bend- 

 ing movements of the body occur so as to increase the ventilation 

 of the lungs. Finally, in the distress of asphyxiation there is 

 hardly a muscle in the whole body that is not pressed into the 

 service of supplying this absolutely vital oxygen to the blood. 



That means that most of the organs of the animal body can 

 act vicariously. When one kidney or lung is diseased, the other 

 responds to the strain on the system, becomes bigger, and takes 

 over some of the work that its partner formerly did. The lungs, 

 skin, and kidneys all excrete water, and if one of the three is 

 diseased and cannot properly function, the others increase their 

 activities. When there is local infection by bacteria, the phago- 

 cytes of the blood, which are, normally, fairly evenly distributed 

 throughout the body, now crowd to the injured place and seek 

 to destroy the intrusive organisms. And so on; it is one for all, 

 and all for one. In the healthy animal the activity of any one 

 organ is regulated by those of all the others to produce a harmony 

 of action in which there are really no distinct parts. 



Inco-Ordination of Activities. — But there is also disease and 

 pain, and we must enquire into the meaning of these conditions. 

 In the healthy animal every part of the body is in nervous con- 

 nection with the brain and spinal cord, and a multitude of 

 impulses are continually streaming from the tissues to the central 

 nervous system. Generally we do not attempt to make an 

 analysis of this undeveloped sensation, and it blends to produce 



, a vague but satisfactory feeling of normality, and that is (as we 

 shall see later) because all these impulses entering the centres 

 from the periphery are answered or receive appropriate responses. 

 They are verified, co-ordinated, integrated. If they are not, if 

 there are insistent impulses from the tissues that do not end in 

 suitable responses, there is pain. The vague feeling that dinner- 

 time is approaching passes insensibly into hunger — a stimulus 

 which ought to find its response in an act of eating. If it does 

 not, if the stimulus remains unanswered, we recognise it as pain. 

 Disease is more than this ; it is a disharmony, a disturbance of 



,the general, unified functioning of the body — the indication of 

 truly partial activity. If there is individualised, uncontrolled 



