x VASCULAE MUSCLE AND NERVES 357 



dilatation of the same vessels is obtained when the posterior roots 

 of the eleventh and twelfth dorsal nerves are stimulated, because 

 in that case the excitation is conveyed by the anterior roots of 

 the same, which, as we have seen, contain dilator fibres (Bradford). 



The vascular reflexes may extend from one side to the other of 

 the body. On central excitation of the sciatic, the paw on the 

 opposite side becomes warmer (Masius and Vanlair) ; stimulation 

 of the nasal mucosa dilates the vessels of the whole head, but more 

 decidedly on the excited side (Frangois-Franck). 



The vascular reflexes in man have also been investigated. 

 When one hand is dipped into cold water, the vessels of the other 

 hand contract (Brown-Sequard). On electrical excitation of one 

 limb the vessels of the opposite side contract (Maragliano). 



FIG. 1 (33. Plethysmograms of hand (M) and foot (P) recorded from healthy subject in re- 

 cumbent and motionless posture. (Fano.) The abscissa S, traced with a Deprez signal, in- 

 dicates at B the moment of electrical excitation of the, skin. The line D is traced by a 

 tuning-fork vibrating at 10 vibrations p,er second. 



Fano has also experimented 011 the vascular reflexes of man, 

 using an air plethysmograph, by which he was able to record 

 simultaneously the pulse and the changes in volume of the hand 

 and foot. He came to the following conclusions : the reaction 

 time of the vessels is always very long ; it oscillates between two 

 and seven seconds, according to the conditions in which the subject 

 of the experiment is placed, and the part of the body stimulated. 

 The vascular constriction consequent on a stimulus is always more 

 pronounced in sleep than in waking. The reaction time is longer 

 in sleep than in waking. The reaction always occurs, inde- 

 pendent of the point of stimulation, first in the upper and then 

 in the lower extremities. In the latter, however, the constriction 

 is more persistent (Fig. 163). 



