THE CIRCULATION OF THE BLOOD AND LYMPH 163 



marked : the cutaneous vessels are widely dilated and 

 engorged, the face is livid, but the abdominal organs are 

 pale and bloodless (Heidenhain). The blood-pressure rises 

 rapidly, reaches a maximum, and then gradually falls as the 

 vaso-motor centre becomes paralyzed (Figs. 56 and 57). 



These facts enable us to some extent to understand the 

 manner in which the distribution of the blood is adjusted to 

 the requirements of the different parts of the body, so that 

 to a certain degree of approximation no organ has too much, 

 and none too little. The blood-supply of the organs is 

 always shifting with the calls upon them. Now, it is the 

 actively-digesting stomach and the actively-secreting glands 

 of the alimentary tract which must be fed with a full stream 



FIG. 56. RISE OF BLOOD-PRESSURE IN ASPHYXIA (IN RABBIT). 



Respiration stopped at r. Interval between 2 and 3 (not reproduced) 44 seconds, 

 during which the blood-pressure steadily rose. At 4, respiration resumed. Time 

 tracing marks seconds. 



of blood, to supply waste and to carry away absorbed nutri- 

 ment. Again, it is the working muscles of the legs or of the 

 arms that need the chief blood-supply. But wherever the 

 call may be, the vaso-motor mechanism is able, in health, 

 to answer it by bringing about a widening of the small 

 arteries of the part which needs more blood, and a compen- 

 satory narrowing of the vessels of other parts whose needs 

 are not so great. 



It is also through the vaso-motor system, and especially 

 by the action of that portion of it which governs the 

 abdominal vessels, and of the nerves that regulate the work 

 of the heart, that in animals to which the upright position 



II 2 



