BY DR. BURDON-SANDERSON. 333 



curial column usually rises above the normal, but after it is 

 over, subsides to a height which is nearly the same as that 

 about which it oscillated before artificial respiration was sus- 

 pended. The explanation of these phenemena may be given in 

 a few words. One of the effects of diminishing the proportion 

 of oxygen in the circulating blood is to excite the vasomotor 

 centre, and thus determine general contraction of the small 

 arteries. The immediate consequence of this contraction is to 

 fill the venous S3 r stem, in the production of which result the 

 contraction of the expiratory muscles of the trunk and extremi- 

 ties powerfully co-operates. The heart being abundantly sup- 

 plied with blood, fills rapidly during diastole and contracts 

 vigorously, in consequence of which and of the increased resist- 

 ance in front, the arterial pressure rises. This last effect is 

 however temporary ; the diastolic intervals being lengthened 

 by the excitation of the inhibitory nervous system, and the 

 heart itself weakened by defect of oxygen, the organ soon 

 passes into the state of diastolic relaxation already described. 

 Its contractions become more and more ineffectual till they 

 finally cease, leaving the arteries empt\ r , the veins distended, 

 its own cavities relaxed and full of blood. That the small arte- 

 ries are contracted in asphyxia we learn by inspecting them 

 (see 49). The narrowing is as marked as it is during elec- 

 trical excitation of the medulla oblongata. In both cases the 

 contraction induces increased arterial pressure, but there is 

 this difference, that whereas in the latter case the heart is not 

 interfered with, in the former its functional activity is much im- 

 paired by the condition of the blood. Consequently, the rise 

 of the arterial pressure is much greater in proportion to the 

 degree of contraction of the arteries during excitation of the 

 medulla than in asphyxia. 



112. Examination of the Heart after Death by 

 Asphyxia. If the heart is rapidly exposed immediately 

 after death by asphyxia, and a strong ligature tightened round 

 the roots of the great vessels, the organ may be readily cut 

 out without allowing any blood to escape from its cavities. 

 The quantity of blood contained in the right and left side re- 

 spectively may be measured by carefully opening the ventri- 

 cles and allowing their contents to flow into separate measure 

 glasses. It is always found that all the cavities of the heart 

 are filled to distension, the quantities in the right and left 

 cavities respectively, usually being to each other about in the 

 proportion of 2 to 3. The lungs are always pale ; if, however, 

 the body is kept for a few hours, those parts of the organs 

 which are lowest becomes airless and soaked with sanguino- 

 lent liquid. 



113. Demonstration of the Chemical Changes which 

 occur in the Blood in Dyspnoea and Asphyxia. It 



