POWER OVER METABOLISM. 455 



we have described, but in many respects still very obscure. 

 Thus the proteids are not at once broken down into 

 carbonic acid, water, and nitrogenous compounds, as repre- 

 sented above. In some of the tissues at least there are inter- 

 mediate products, one of which is fat, which is in turn oxydised 

 into carbonic acid and water. It is also probable that all 

 metabolism is associated with ferments, if not actually due 

 to their activity, like digestion and the coagulation of the 

 blood. Lastly, the intimate protoplasmic changes which are 

 the basis of vital force are controlled by the central nervous 

 system, by trophic centres lying in the cord and cerebrum, 

 with afferent and efferent trophic nerves. 



II. PHARMACODYNAMICS. 



This brings us to the second part of our inquiry our power 

 over metabolism in a healthy individual. This is greater than 

 would at first appear. 



1. Our influence on metabolism through the blood as a whole, 

 has been fully discussed in the preceding chapter, and does 

 not require to be more than mentioned here. 



2. We can affect nutrition through the constituents of the 

 blood which supply material to the particular organs. Ex- 

 perience taught us, long before science, how to feed a man in 

 training for muscular exertion ; which kinds of food are specially 

 suited for the exercise of the brain, for the periods of growth 

 and development, of pregnancy and lactation, of degeneration 

 and decay. It is but expressing the same fact in other words 

 to say that by supplying an excess of certain kinds of food, 

 we can increase the activity of an organ, the cells of which 

 appear to exercise themselves more vigorously when their 

 natural source of energy and nutrition is freely supplied 

 to them. Alcohol, Cod-liver Oil, Olive and Almond Oils are 

 thus valuable foods, or nutritive tonics. 



3. An increased supply of oxygen in the blood increases 

 metabolism. The valuable influence of fresh air on active 

 organs is familiar, and we have learned in this connection 

 the use of Iron, which is thus a hsematinic tonic. 



4. An increased amount of work is an interesting means of 

 increasing protoplasmic activity. By throwing more weight 

 upon a muscle, up to a certain point, we can increase the force 

 of its contraction. This is exercise ; but it must be accompanied 

 by a sufficient supply of plasma and oxygen. A man in 

 training not only selects his food and air, but throws an in- 

 creased amount of work on his muscles by exercising them 

 regularly. 



