348 EFFECT OF WARMTH, AND OF ALCOHOL. [BOOK i. 



arteries, which is produced by external warmth, is probably 

 another instance of diminished activity of tonic constrictor in- 

 fluences ; though the result, that the dilation produced by warm- 

 ing an animal in an oven is greater than that produced by section 

 of nerves, seems to point to the dilator fibres for the cutaneous 

 vessels which, as we have seen, probably exist in the sciatic 

 and brachial plexuses and possibly in all the spinal nerves, also 

 taking part in the action. A similar loss of constrictor action 

 in the cutaneous vessels may be the result of certain emotions, 

 whether going so far as actual blushing of the body, or merely 

 producing a 'glow.' The effect of cold on the other hand, and 

 of certain emotions, or of emotions under certain conditions, 

 is to increase the constrictor action on the cutaneous vessels, 

 and the skin grows pale. It may be worth while to point 

 out, that in both the above cases, while both the cold and 

 warmth produce their effect, chiefly at all events through the 

 central nervous system, and very slightly, if at all, by direct action 

 on the skin, their action on the central nervous system is not 

 simply a general augmentation or inhibition of the whole vaso- 

 motor centre. On the contrary, the cold, while it constricts the 

 cutaneous vessels, so acts on the vaso-motor centre as to inhibit that 

 portion of the vaso-motor centre which governs the abdominal 

 splanchnic area ; while less blood is carried to the colder skin, by the 

 opening up of the splanchnic area more blood is turned on to the 

 warmer regions of the body, and the rise of blood-pressure which 

 the constriction of the cutaneous vessels tended to produce, and 

 which might be undesirable, is thereby prevented. Conversely 

 when warmth dilates the cutaneous vessels, it at the same time 

 constricts the abdominal splanchnic area, and prevents an un- 

 desirable fall of pressure. 



The warm and flushed condition of the skin, which follows the 

 drinking of alcoholic fluids, is probably, in a similar manner the 

 result of an inhibition of that part of the vaso-motor centre which 

 governs the cutaneous arteries; and it is probable also, that 

 except for the local effect of the fluid on the gastric mucous 

 membrane, whereby some amount of blushing of the gastric blood 

 vessels takes place as a reflex act, this effect on the vessels of 

 the skin is accompanied by an inverse constrictor action in the 

 splanchnic .area. This last point however has not been proved 

 experimentally and may not occur, since the influence of the 

 alcohol is at the same time to increase the heart's action, and thus 

 to obviate the fall of pressure which would certainly occur were 

 the cutaneous and splanchnic vascular areas to be dilated at the 

 same time. This effect of the alcohol on the heart may be a 

 direct action of the alcohol on the cardiac substance, being carried 

 thither by the blood ; but the effect, in being an augmentation 

 of the force and acceleration of the pace of the heart-beat of 

 a temporary character, followed by a reaction in the direction 



