250 HUMAN BIOLOGY 



INTEGRATION BY PURE REFLEX ACTION 



In the lower vertebrates the spinal cord forms relatively 

 to the brain a much larger portion of the whole central 

 nervous organ. Spinal reactions unaided by the brain operate 

 a much larger part of the acts of the animal than in higher 

 forms. There is no evidence that mental experience enters 

 into any of this spinal operation; its reactions appear to 

 follow mechanically and automatically, and for that very 

 reason are termed reflex. This "spinal" life concerns itself 

 in these animals with attitude, locomotion, breathing move- 

 ments, movements for grooming the skin, and defending 

 it from parasites, movements of escape from local injury, 

 the actual swallowing of food, and so on. The reflex actions 

 thus exhibited are themselves of various grades of com- 

 plexity. Reflex actions of various grades such as obtain in 

 animals make up also a large part of the functioning of the 

 nervous system of man. Integration by reflex action is a 

 part of the integration which his nervous system effects 

 for man, and an important part. His reflexes perform many 

 sorts of useful acts for him throughout his waking day, not 

 to speak of some, such as his reflex breathing, which continue 

 during his profoundest sleep. This "reflex" life of man 

 is sufficiently many-sided to reheve the mental portion of 

 his nervous system from much that, were matters not so, 

 would occupy it and preclude his attention, one would 

 suppose, from higher things. 



Of this reflex life one field which is particularly primitive 

 is that concerned with the viscera, particularly the digestive, 

 and their movements. Such movements, though rather 

 complex, occur with digestive periodicity, largely regulated 

 by lower and primitive centers of the nervous system, 

 and during health they pass practically unperceived, indeed 

 the mind cannot by any eff"ort of attention attain perception 

 of them. Another related primitive reflex or set of reflexes 

 concerns the movements which, ventilating the lungs, are 

 indispensable for breathing. These, although themselves 

 in essence purely automatic, illustrate the close touch which 

 can obtain between the "reflex" and the "mental." We can 

 hardly think about our respiratory movements without 



