178 THE BLOOD AND ITS CIRCULATION. 



according to Schiff, differing in animals of the same kind, 

 under different circumstances. 



As the vaso-motors spread into the arteries, they follow an 

 independent course in certain parts, as in the neck and head, 

 where the sympathetic nerve, even in its secondary plexus, is 

 detached from the nervous system which presides over the 

 organic processes ; in other cases, their arrangement exactly 

 resembles that of the arterial branches (abdominal sympa- 

 thetic) ; or, finally, as is the case with the limbs, they unite 

 and are lost in the nerves of the brachial and lumbar plexus, 

 etc., the union being made at the level of, or at a certain 

 distance from, the plexus ; in the case of the sciatic nerve, a 

 little before it leaves the pelvis, and in the nerves of the 

 arm, at the level of the brachial plexus (Claude Bernard). 



The modifications caused in the circulation by the func- 

 tions of the vaso-motor nerves, are extremely important when 

 considered in reference to the phenomenon of secretion and 

 calorification (see animal heat, farther on). These modi- 

 fications should be also closely studied in regard to many 

 pathological phenomena. Thus fever is owing, in a great 

 measure, to a derangement of the vaso-motor nerves paralyz- 

 ing the vessels, and producing a change in the regulation of 

 the heat of the body. A remarkable disagreement may also 

 sometimes be observed between a local disease and the fever 

 which accompanies it. The latter may break out, or cease sud- 

 denly, by a modification which is in some respects dynamic 

 (nervous system), while the disease must run its course 

 through all the phases of cellular and vegetative growth 

 (Hirtz). 



In order to complete the history of the vaso-motor nerves, 

 it would, finally, be necessary to review the numerous thera- 

 peutical applications by which these modifications may be 

 produced, but we will mention one only of this class of 

 medicaments, digitalis ; this substance has the effect of 

 lowering the pulse and diminishing heat, and is, therefore, a 

 powerful agent against fever, the pathological physiology of 

 which may be briefly stated in these few words. Besides 

 retarding and regulating the motion of the heart, digitalis 

 also acts on the peripheral organs of the circulation, causing 

 contraction of the coats of the arteries, by exciting the vaso- 

 motor nerves (Ackerman). When slackened by digitalis, 

 the pulse becomes stronger and fuller. The tension of the 

 arteries appears to increase, and the special power of this 



