REGULATION OF BREATHING 3 
that we must look to a more thorough and direct 
interpretation.t 
Breathing is a form of physiological activity which 
goes on whether we are conscious of it or not. Only 
by a great effort can we suspend it for 30 or 40 sec- 
onds, and any hindrance to breathing is violently 
resisted. Although in the seventeenth century Mayow 
came very near to discovering the chemical changes 
in air during breathing, it was not till the latter half 
of the eighteenth century that these changes were 
understood. Black found that what we now call 
carbon dioxide is given off in breathing, and Priestley 
found that what we now call oxygen disappears as 
such. Lavoisier put these and many other facts 
together, and showed that just as in ordinary com- 
bustion of carbonaceous material, so in connection 
with respiration, oxygen combines with carbon and 
hydrogen to form carbon dioxide and water, and to 
liberate heat. Hence breathing is a process in which 
the essential factors are the conveyance of oxygen into 
the body, and the removal from it of carbon dioxide. 
Breathing can thus be compared to the supply of air 
to a fire and the carrying off by the air of the products 
of combustion. 
Subsequent investigation showed that the oxidation 
1Tt has been suggested to me that if a convenient label 
is needed for the doctrine upheld in these lectures the word 
“organicism” might be employed. This word was formerly 
used in connection with the somewhat similar teaching of 
such men as Bichat, von Baer, and Claude Bernard. Cf. 
G. Delage, L’Hérédité, Paris, 1903, p. 435. 
