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[Vol. IX., No. 212 



vessels, the muscle-substance, by virtue of its 

 chemical affinities, extracts certain matters from 

 the supply-fluid, and recovers its irritability and 

 contractility. Now, we know that this unstable 

 muscle-substance is continually being oxidized 

 with the production of certain waste products. 

 Suppose that the affinities of a given muscle-fibre 

 for food matter are so feeble that less nutriment is 

 brought in a given time into the tissue than is lost 

 in the way of waste : the result is a gradual de- 

 cadence or atrophy of that muscle. As in the 

 physiological condition the food-supply is limited, 

 those muscle-fibres with strongest constructive 

 chemical affinities rob the weaker fibres, which 

 could only get their fill, as it were, by a modifica- 

 tion of physiological activity throughout the whole 

 body. This explanation of the relation of growth 

 to competition probably partly underlies the well-, 

 known fact of the extraordinary growth of one of 

 a pair of similar organs, as a kidney, when its 

 fellow is extirpated. 



Owing to the physiological division of labor 

 among the tissues, each one of these has come to 

 depend nearly absolutely upon organs far removed 

 for some of the essentials to its welfare : as, for 

 example, a gland is often called upon during secre- 

 tion to pour out a bulk of material greater than its 

 own volume, and for the performance of this 

 function there is an alteration of vaso-motor 

 activity through which more blood visits the gland 

 in time of need ; and this vascular change, as also 

 the secretion itself, is directly controlled by nerve- 

 centres lying in the distant brain. So, elsewhere 

 in the body, we are continually coming upon 

 phenomena in which the working tissue appears 

 to derive little direct benefit from its effort ; the 

 activity of each organ seems determined by, or at 

 least co-ordinated with, the needs of its fellows ; 

 and this fact, indeed, constitutes the very defini- 

 tion of physiological activity. 



If we invent a physiological allegory, whose 

 personages are the animal cells supposed to be en- 

 dowed with sensibility, reason, and motion, like in 

 kind to the faculties of complete organisms, we 

 should find that the fanciful sketch of the cellular 

 society constructed on such a scheme corresponds 

 remarkably well, if not identically, with the actual 

 result of such associations of cells as we find 

 them in living organisms. The apparent altruism 

 noted above is perhaps most marked in the work- 

 ing of the respiratory nerve-centre on whose 

 rhythmic impulses directly depends the contraction 

 of the respiratory muscles which expand the 

 chest, and thus draw into the lungs the fresh air 

 necessary to the life of the whole body. 



This nerve-centre is generally supposed to be 

 composed essentially of a group of nerve-cells oc- 



cupying an insignificant area of the brain ; and on 

 their ceaseless, rhythmic output of energy every 

 living molecule of the body each moment derives 

 benefit without giving any manifest adequate re- 

 turn. Still, though each new study of the body 

 brings to view fresh examples of the subservience 

 of individual needs of the physiological units to 

 the welfare of the community of cells, it can be 

 shown as scarcely doubtful that this altruism, ap- 

 parently purposive on the part of the living in- 

 tegers, is but an indirect outcome of an effort for 

 their own aggrandizement, their supreme selfish- 

 ness, as it were. There is the strongest reason to 

 believe that the physiological individual, or cell, in 

 a complex organism, is primarily as completely bent 

 upon its own nutritive welfare, and as regardless 

 of the condition of its neighbors, as if it were a 

 free monad contending for sustenance against a 

 myriad of its fellows in a culture-solution. Even 

 in the case of the action of the respiratory centre, 

 which seems devoted purely to aims benevolent 

 to the organism as a whole, experiment indicates 

 that any such benefit conferred outside the centre 

 itself is, as it were, a mere accident in its ac- 

 tivity. 



It is the present belief of physiologists that the 

 nerve-cells of the respiratory centre are stimulated 

 by a lack of oxygen to discharge energy into the 

 motor nerves arising from them ; and their dis- 

 charges, up to a certain point, increase in vigor 

 with diminution of oxygen-supply, and conversely 

 become weaker and less frequent when that gas 

 is in excess in the blood. If oxygen fail totally, 

 the cells soon die. Now, suppose an animal to be 

 in a state of respiratory quiescence : oxygen is 

 still being drawn from the blood by every living 

 tissue. ,As a result of this, there is failure of oxy- 

 gen in the respiratory centre ; and a stimulus of 

 some sort is heaped up in the nerve-cells there, 

 until finally an explosion of energy proceeds from 

 them into their motor nerves, and thence to the 

 muscles of inspiration which cause the chest to 

 expand. Thereby fresh air is drawn into the lungs, 

 new oxygen diffuses into the blood, and thus the 

 excitement of the respiratory centre is allayed for 

 a while, presumably owing to the oxidation in the 

 centre of some irritating chemical products of 

 tissue-change. 



It has been found, that, if the manner of circu- 

 lation is artificially so altered in a living animal 

 that the brain still receives blood oxidized to its 

 normal arterial condition, while tissues of the 

 trunk or limbs get only venous blood or even none 

 at all, the rhythmic action of the respiratory 

 centre goes on undisturbed, though the organs 

 with altered circulation soon die from asphyxia. 

 On the contrary, should the arteries conveying 



