ANIMAL ELECTRICITY. LECTURE II. 49 



or in the blood, or in the tissues, and straightway run 

 down hill together — I think the phrase " respiration 

 is a slow combustion " is permissible. Oxygen, the 

 incoming "food" — for oxygen is even a more imme- 

 diately necessary " food " than water, bread and meat — 

 first climbs a mountain where it is lost to view, as a 

 member of that mysterious company of atoms we call 

 ''proteid,"^ which have power to act, which by acting 

 are expended, yielding to the body movements that 

 are the expression of its life, heat which is a sine qua 

 lion of its action, and carbon dioxide which is the 

 token and measure of its activity. 



The immediate antecedent of physiological activity 

 is chemical change — a disintegration of "inogen," of 

 which at least one end-product is carbon dioxide. 

 Living tissue is deoxydative or reducing towards the 

 oxygen-yielding blood by which it is traversed ; it is 

 at the same time oxydative and synthetic as regards 

 the formation of its own working balance of inogen, 

 deoxydative and analytic as regards expenditure of 

 that balance. It is a maxim of political economy that 

 imports equal exports ; a similar maxim applies to the 

 organism and to any portion of the organism that is to 

 maintain itself in the physiological economy. If a 



^ Perhaps it would be better to say '' inogen," in order not 

 to seem to prejudge the vexed question whether the force- 

 producing compound that disintegrates is proteid or carbo- 

 hydrate. 



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