ON THE NATURE OF ANIMAL LIFE 5 



Think about it carefully, and we find that the normal, healthy 

 man or woman has no intuitive knowledge of the separate 

 activities of the parts of the body. Most of us are (or ought to 

 be) quite unconscious that we possess stomach and liver and 

 lungs, and so on, for all these organs are acting together and form 

 a harmony. We assume that these parts are in us because of 

 our knowledge of the structure of the bodies of other animals, 

 but, lacking that knowledge, it is unlikely that we should be 

 able to make an analysis of the activities of our own bodies. It 

 requires some effort of concentration to convince a healthy man 

 that he possesses a liver and stomach. It is true that he would 

 be periodically conscious of a " feeling " of hunger, but that 

 would be something quite different from the empirically acquired 

 knowledge that his stomach was empty. 



Integration of Activities. The healthy living animal is one 

 and indivisible, and the more deeply we study physiology the 

 more clearly do we see that no organ functions by itself and for 

 itself at least, not in the healthy animal. Let us illustrate this 

 by considering the process of respiration. Concentrating our 

 attention on this phase or aspect of our living activity, we find 

 that the chest wall rises and the diaphragm sinks, and so the 

 cavity of the chest is enlarged. But the lungs fill this cavity; 

 they are distensible, and so air rushes into them to fill up the 

 extra space produced by the act of inspiration. Next, look at 

 the composition of the air inhaled and exhaled; it is different in 

 respect of the percentage of oxygen that it contains, and so we 

 find, on further investigation, that oxygen is taken into the 

 blood- stream via the lungs, and is then carried all over the body. 

 At the same time nutritive material is being taken by the blood 

 from the alimentary canal, and is being distributed over the body, 

 and is built up into the substance of the tissues, where it meets 

 with the oxygen that comes from the process of respiration and 

 is oxidised. This oxidation sets free energy, which is then trans- 

 formed into the mechanical work done, and the heat generated 

 by the muscles. But the muscles themselves are being employed 

 to activate the respiratory machinery that supplies them with 

 the indispensable oxygen. 



Now, imagine that the percentage of oxygen in the air is 

 becoming much less than is normal, and that the percentage of 

 carbonic acid gas is increasing; at once everything changes. 

 The respirations become quicker and deeper, and the heart's rate 



