105 



which would have only slight and quite different effects in 

 the waking state may call forth complex and pronounced 

 reflex responses. The influence of afferent impulses in 

 provoking and shaping the course of dreams need not be 

 emphasized. Potent in this respect are impulses from the 

 viscera which in the waking state would only be productive 

 of slight sensations of discomfort— headache, nausea, etc. ; 

 in sleep elaborate responses may be set up, especially when 

 unrestrained emotional processes are called into action 

 with their resultant effects on both cerebro-spinal and 

 autonomic innervation — excitation of • sympathetic, etc. 

 Such emotional excitation is apt to reach a high grade of 

 intensity from lack of the balance and restraint normally 

 exercised by the fully active mechanisms of ordinary con- 

 sciousness, especially by those subserving the higher levels 

 of mental function acquired through experience after the 

 infantile stage of life. 



The suddenness of development of the functional distui'b- 

 ances in blood pressure, heart action, etc., in the dreaming 

 state is an important feature. As is well known, most 

 dreams are of very brief duration as regards the actual 

 time occupied, a number of seconds or a very few minuted 

 often sufficing for a dream which is subjectively a long and 

 complicated one — for example, an apparently long and 

 varied dream has been recorded as running its course 

 between the beginning and the ending of a clock striking 

 midnight. The associated functional disturbances may thus 

 be set up with unusual abruptness, as compared with the 

 waking state — as, for instance, in ordinary muscular exei'- 

 cise. It follows that there is little or no time for the 

 coming into play of the various adjustments and compensa- 

 tions in the circulatory and respiratory systems, etc., that 

 are operative in muscular exercise ; in the latter the rise of 

 arterial pressure is checked by gradual dilatation of the 

 vessels of the skin and the working muscles, while the 

 heart accommodates itself with the aid of increased 

 coronary blood supply, etc. Thus the blood pressure rise 

 in certain dreams may be both large and steep in ascent. 

 The call on the heart, through its nervous apparatus, etc., 

 may also be a sudden one. 



Influence of the Recumbent Posture. 



So far as the rupture of a weakened cerebral artery is 

 in question the hydrostatic factor in the recumbent 

 position is an added consideration ; the weight of the 

 column of blood between the levels of the head and the 

 heart, which reduces the cerebral artery pressure in the 

 standing position, is now largely out of action ; with a 

 given aortic pressure the pressure in a cerebral artery is 

 naturally higher by a very appreciable amount (varying 

 according to the elevation of the head) in the recumbent 

 than in the erect posture, and the danger of a cerebral 



