REFLEXES 57 



theless, frank and intelligent people can often furnish 

 illustrations. The most frequent are probably connected 

 with the large intestine and the bladder. Certain condi- 

 tions which have no logical bearing upon the functions of 

 these organs will regularly arouse them to inconvenient 

 activity. A friend of the writer cannot mislay an article 

 and begin to search for it without having an immediate 

 awakening of the colon to energetic movement. On some 

 occasion in the past there was probably a coincidence of 

 the two circumstances and a cross-tie between two 

 mechanisms has remained. Such a tie has undoubtedly 

 an anatomic existence, though we do not expect to have it 

 pointed out postmortem in the mazes of the brain. Out- 

 breaks of perspiration in certain circumstances may be 

 explained in similar ways. 



Summary. The salient facts regarding reflex action 

 may now be concisely stated. Reflexes are adaptive reac- 

 tions brought about by the influence of stimuli acting 

 upon the receptors of the nervous system. For their 

 execution five conditions must be fulfilled: (1) The end- 

 organs, or receptors, must be ready to translate the 

 energy applied from without into nerve-impulses. (2) 

 There must be pathways open for the conduction of these 

 impulses to the gray matter of the central axis. (3) The 

 central gray matter must have such an organization and 

 such a degree of irritability that the arrival of the afferent 

 impulses shall determine the departure of efferent im- 

 pulses along definite paths. The fitness of the reflex to 

 the emergency, as commonly observed, is explained by the 

 physiologic linkage of certain afferent with certain efferent 

 channels in the cord and brain. (4) There must be lines 

 of effective communication between the central stations 

 and the end-organs of the efferent system, namely, 

 muscles and glands. (5) These organs must be capable of 

 modifying their activity upon the arrival of the outflow- 

 ing impulses. The change induced may be in the direc- 

 tion of increased activity or the reverse excitation or 

 inhibition. 



