102 



burst at that time? A similar question has to be dealt 

 with in the case of pulmonary haemorrhage, which, as is 

 well known, is frequently nocturnal in its incidence. The 

 same applies to gastro-intestinal haemorrhages. 



It is, of course, a matter of familiar knowledge that true 

 anginal pain occurring in the daytime is commonly asso- 

 ciated with exertion or excitement involving raised blood 

 pressure and an increased call upon the heart, the pain 

 diminishing or passing off with cessation of the muscular 

 effort or emotional disturbance, reduction of the blood 

 pressure by amyl nitrite, etc. But it is also well known 

 that anginal pain sometimes seizes the patient in the quiet 

 of the night, awakening him from sleep. What is to be put 

 down as determining the onset in these cases? 



Again, we know that sudden death in the night is not 

 rare, sometimes coming thus to persons who have shown 

 little or no evidence of serious departure from the level of 

 their ordinary health, or at least nothing to warrant the 

 expectation of so sudden a termination. In a former paper 

 considerations were advanced in support of the view that 

 the usual mechanism of such deaths is to be found in 

 fibrillation of the ventricles, occurring in a heart which 

 has become specially susceptible as a result of defective 

 coronary blood supply, degenerative changes, toxic 

 influences, etc. , But, granted such predisposition, what 

 is the exciting cause that precipitates the sudden and 

 unforeseen disaster in the night-time? 



Becognition of Two Different Conditions in Sleep. 

 The results obtained in the present investigation lead 

 to the conclusion that m considering the subject of 

 sleep we have to deal with two distinct conditions, which 

 have strikingly different associations as far as nervous, 

 circulatory, respiratory, and other functions are concei'ned : 

 (1) undisturbed or sound sleep, attended by lowering of 

 blood pressure, heart and respiratory rates, etc., and (2) 

 disturbed sleep, modified by reflex excitations, dreams, 

 nightmare, etc., sometimes accompanied by extensive rises 

 of blood pressure (hitherto not recognized), increased heart 

 action, changes in respiration, and various reflex effects. 

 The circulatory changes in disturbed sleep are sometimes 

 so very pronounced that it is somewhat remarkable that 

 they should so long have escaped observation. So far as 

 the present writer knows, the occurrence of marked rises 

 in blood pressure during sleep has not even been suggested 

 — apart from the fact that no actual measurements have 

 been recorded. No doubt paucity of opportunities and 

 diflBculties in observation have stood in the way. But the 

 considerations as regards the occurrence of haemorrhages, 

 etc., in the night (stated in the earlier part of this paper) 

 give distinct indications of the probability of important 

 blood pressure changes being present in some instances. 



