506 THE VASCULAR SYSTEM. [Book ii. 



pressure ; that is obviously due to a very great increase of periph- 

 eral resistance, the heart contributing to the result only so far 

 that its output does not diminish as the peripheral resistance 

 increases, or indeed may at first, at least, somewhat increase. 

 That the peripheral resistance is due to a large vaso-constriction 

 brought about by the too venous blood stimulating the bulbar 

 vaso-motor centre is shewn by the fact that the rise of pressure 

 is far less, indeed very small, if the cord be divided below the 

 bulb ; only a small part, at most, of the peripheral resistance 

 can be attributed to the difficulty which the blood, on account 

 of its increasing venosity, finds in passing through the capil- 

 laries (§ 163). 



If a limb be placed in a plethysmograph during this rise of 

 pressure, its volume is found to increase ; and the same is true 

 of the brain. This shews that the vaso-constriction does not 

 take place to any great extent in the skin (or the muscles) of 

 the limb or in the brain. No such increase of volume is seen 

 in the kidney or other abdominal organs. Hence we may con- 

 clude that the vaso-constriction is, in the main, one of the 

 splanchnic area and not of the skin, or indeed of the rest of 

 the body. 



If the pressure in the pulmonary artery be examined this 

 is found to increase, even out of proportion to the increase of 

 the systemic pressure. We may infer that the peripheral resist- 

 ance in the lungs is very largely increased ; and we may also 

 probably infer that the resistance is due to vaso-constriction, 

 though possibly the too venous blood may find increased diffi- 

 culty in traversing the pulmonary capillaries. 



The high arterial pressure both on the left and right sides 

 leads to great distension of the ventricles, and this is still 

 further increased on the right side by the large quantity of 

 blood which the high systemic pressure is able to discharge 

 into the venae cavse through the vascular areas in which no 

 vaso-constriction is taking place. 



These then are the main features of the circulation during 

 asphyxia (under urari) : high systemic pressure due chiefly to 

 vaso-constriction in the splanchnic area; high pulmonary pres- 

 sure due to high pulmonary resistance, working against an 

 ample supply of venous blood to the right ventricle; a heart 

 beating slowly, but with increased output, and increasing dis- 

 tension of both ventricles (leading to distension of the auricles) 

 but greater perhaps on the right side. 



This state of things however lasts for a certain time only; 

 the blood-pressure soon begins to fall, and falling rapidly soon 

 becomes very low. The diminished energy of the heart-beats, 

 the output at the systole diminishing greatly though the dia- 

 stolic distension remains, is sufficient to account for this fall; 

 and indeed that the fall is not due to lessening of the periph- 



