THE CIRCULATION OF THE BLOOD AND LYMPH 175 



the general arterial pressure, while it need not be feared that 

 transfusion of a considerable quantity of blood, or of salt solu- 

 tion, in cases of severe haemorrhage will dangerously increase 

 the pressure. And from the physiological point of view the 

 term ' haemorrhage ' includes more than it does in its ordinary 

 sense. For as dirt to the sanitarian is ' matter in the wrong 

 place/ haemorrhage to the physiologist is blood in the wrong 

 place. Not a drop of blood may be lost from the body, and yet 

 death may occur from haemorrhage into the pleural or the 

 abdominal cavity, into the stomach or intestines. Not only so, 

 but a man may bleed to death into his own bloodvessels ; in 

 surgical shock, as well as in ordinary fainting or syncope, the 

 blood which ought to be circulating through the brain, heart and 

 lungs may stagnate in the dilated vessels of the splanchnic and 



FIG. 73. BLOOD-PRESSURE TRACING FROM A DOG POISONED 

 WITH ALCOHOL. 



The respiratory centre being paralyzed, respiration stopped, and 

 the typical rise of blood-pressure in asphyxia took place. The pres- 

 sure had again fallen, and total paralysis of the vaso-motor centre 

 was near at hand, when at A the animal made a single respiratory movement. 

 The quantity of oxygen thus taken in was enough to restore the vaso-motor centre, 

 and the blood-pressure again rose. This was repeated five or six times. (Three- 

 fourths original size.) 



other areas. The rapid feeble pulse in shock is due to a similar 

 loss of activity of the cardio-inhibitory centre. The cause of the 

 vascular symptoms of surgical shock is by no means clear, and 

 is probably complex. Some observers have laid stress upon the 

 supposed effect of excessive stimulation of afferent nerves in 

 producing long-continued inhibition or fatigue of the vaso-motor 

 centres. In favour of this hypothesis is the fact that in experi- 

 mental shock in animals the rise of blood-pressure which can be 

 obtained by stimulation of a nerve like the sciatic is not so great 

 as under normal conditions (Crile, Howell). As already men- 

 tioned (p. 169), a diminution of the carbon dioxide pressure in 

 the blood occasioned by increased pulmonary ventilation due to the 

 excitation of afferent nerves, or in the case of abdominal opera- 

 tions or wounds by the direct escape of carbon dioxide through 

 the peritoneum, has also been suggested as an important factor. 



