RESPIRATION 391 



work of the heart or lungs. What is maintained in the tissue en- 

 vironment is oxygen pressure in its organic relations. The rela- 

 tivity to one another of the phenomena of life stands out clear in 

 this maintenance of organic identity. 



In the course of biological investigation we meet on all hands 

 with similar examples of maintenance and reestablishment of 

 organic identity ; and the existence of this actively-maintained 

 identity is the scientific basis of practical medicine and surgery. 

 But for the fact that functional as well as structural compensation 

 is constantly occurring, not only under ordinary physiological 

 conditions, but also in cases of injury by disease or accident, and 

 that by observation and experiment we can learn to understand, 

 predict, and aid it, physicians and surgeons would be absolutely 

 helpless. Neither scientific biology nor scientific medicine could 

 be based on the ordinary working hypotheses of physics and chem- 

 istry, since these hypotheses furnish no sufficient means of under- 

 standing and predicting biological phenomena. Biologists, physi- 

 cians, and surgeons are not, and never will be, simply chemists 

 and physicists. 



In physiology we are always dealing with responses to immedi- 

 ate stimuli ; but the responses are evidently determined in relation 

 to the maintenance of organic identity. They are organic responses, 

 and are simply rendered unintelligible when by the common con- 

 fusion in thought running through so much of the present teaching 

 of physiology they are represented as examples of mechanical 

 determination. Such expressions as the "mechanism" of respira- 

 tion, or secretion, or of maintenance of the internal environment 

 generally, are examples of this confusion. On closer examination 

 all the assumed mechanical reactions turn out to be expressions of 

 the organic maintenance which is the subject matter of the bio- 

 logical sciences. 



Biology must take as its fundamental working hypothesis the 

 assumption that the organic identity of a living organism actively 

 maintains itself in the midst of changing external appearances. 

 This identity is not physical identity nor identity of form or 

 chemical composition, but something which we can perceive and 

 trace by exact quantitative investigation just as readily and ex- 

 actly as we perceive and trace physical identity in what we inter- 

 pret as the inorganic world. The science which traces this organic 

 identity is biology. Anatomy or morphology traces it as regards 

 structure, and physiology as regards activity. But since organic 

 structure is only the outcome or expression of ordered activity, 



