456 MATERIA MEDIC A AND THERAPEUTICS. 



5. We can influence metabolism "by means of the excretions, 

 that is, by hastening the removal of its products through the 

 lungs, kidneys, skin, and bowels, as we have already seen in the 

 case of the stomach and liver. The same principle manifestly 

 applies to all the tissues. 



6. The trophic centres are amenable to impressions carried in 

 by their afferent fibres, and such of these fibres as originate in 

 the surface of the body are thoroughly accessible, and ready to 

 convey any influence which we may impress upon them, such as 

 extremes of heat and cold, by means of the cold bath or 

 douche, stimulation by Mustard or Cantharides, and the direct 

 battery current. 



7. The metabolic activity of a part may be increased by cer- 

 tain local measures which are familiar to us, as friction and sham- 

 pooing. The physiological effects of these local alteratives or 

 local tonics are very powerful. Their action is complex, partly 

 direct and partly reflex through the trophic nerves. They cause, 

 first, dilatation of the local vessels, leading to increased 

 circulation in the tissues ; more rapid removal of the products 

 of nutrition by the lymphatics and veins ; and an actual exercise 

 of the tissue elements, e.g. of the muscles, by well-arranged 

 movements. No doubt these effects can be increased by the use 

 of certain local circulatory stimulants, in the form of liniments 

 of Ammonia, Alcohol, Chloroform, and the great group of 

 Volatile Oils of the Turpentine and Camphor series. But, 

 further, these local alteratives and tonics react upon nutrition 

 generally, probably through the nervous system, and greatly 

 stimulate it, improving the appetite and digestion, and rapidly 

 causing an increase in the strength and the weight of the body, 

 and thus become general tonics. The action of poultices, 

 blisters, some forms of electricity, and other local applications, 

 on the nutrition of deeper parts, which is known as counter- 

 irritation, is discussed in chapter xv. 



8. The surrounding temperature has a powerful effect upon 

 nutrition. Heat and cold are universally recognised as being 

 stimulating, enervating, relaxing, tonic or bracing, as the case 

 may be. Water, in every form, from vapour to solid ice, is a 

 convenient means of bringing any temperature that may be de- 

 sired into contact with the tissues, whether directly or indirectly 

 through the vessels and nerves. In other words, we possess, 

 and have greatly elaborated, the means of affecting nutrition 

 by baths and climate, the actions and uses of which are the 

 subjects of balneology and climatology. 



9. Medicines. We have made a further important discovery 

 with respect to our influence over metabolism that we can 

 admit to the organs other than the normal constituents of the 



