CHAP. IL] RESPIRATION, 655 



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 ( 185). 



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; moreover it follows a different curve, rising 

 later and reaching a maximum much later. We may infer that 

 the peripheral resistance in the lungs is very largely increased; 

 and, though possibly the too venous blood may find increased diffi- 

 culty in traversing the pulmonary capillaries, yet, since this rise of 

 pressure is far less when the cord is divided below the spinal bulb, 

 we may also probably infer that the resistance is due to vaso- 

 constriction, the result of impulses leaving the cord, we have 

 reason to think, by certain thoracic nerves, chiefly the 3rd, 4th 

 and 5th, though possibly by others. 



The high arterial pressure both on the left and right sides 

 leads to great distension of the ventricles ; and it has been urged 

 that this is still further increased on the right side by the large 

 quantity of blood which the high systemic pressure is able to dis- 

 charge into the venae cava3 through the vascular areas in which 

 no vaso-constriction is taking place, the high resistance in the 

 splanchnic area more than counterbalancing the low resistance in 

 these ; but this is doubtful. 



These then are the main features of the circulation during (the 

 earlier stages of) asphyxia (under urari) : high systemic blood- 

 pressure due chiefly to vaso-constriction in the splanchnic area ; 

 high pulmonary blood-pressure 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 distension of both ventricles (leading to distension of the 

 auricles also), especially perhaps on the right side. 



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

 The blood-pressure then 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 peripheral 

 resistance through slackening of the vaso-constriction is shewn 



