THE ACTIVE FORCES OF LIVING ORGANISMS 7I 



a contraction of the subcutaneous bloodvessels may 

 be supposed to take place, with the result that the 

 internal blood-pressure and the supply to the internal 

 organs, and presumably to the central nervous system, 

 are increased. After a cold bath, however, every effort 

 is usually made to bring the blood back to the skin, 

 which, of course, implies a slight withdrawal of blood 

 from the nerve centres, so that the latter may be 

 supposed to pass from a higher to a lower state of 

 oxidation. If we exclude the vaso-motor factor in its 

 bearing on the central nervous system, it is rather 

 difficult to understand how a bracing effect can be 

 produced, seeing that the skin, owing to the friction 

 to which it is subjected, receives a more abundant 

 supply of blood after the bath than before. At the 

 same time, though this movement of reaction is one 

 of dilation, there is a general vaso-motor movement 

 on a large scale, and this may give rise to secondary 

 effects. On the other hand, the general effect of cold 

 must be very great, or it would not be possible to allay 

 fever by means of it, and in such cases the aim seems 

 to be to produce a direct effect, and not one depending 

 on reaction. 



It seems highly probable that the contractility of 

 the, arteries is to a great extent dependent on the 

 relative proportions of the two gases — carbonic acid 

 and oxygen — which constitute, as it were, the limits in 

 the movement of contraction ; that is to say, in the 

 movement from a higher to a lower state of oxidation. 

 Although the amount of the former can be increased 



