THE METABOLISM OF THE BODY. 479 
bonic anhydride, water, etc. These are individually to be re- 
garded as the final links in a long chain of metabolic processes 
or rather a series of these. Fats and carbohydrates are repre- 
sented finally as carbonic anhydride and water principally, pro- 
teids as urea. 
.Nitrogenous foods may be regarded as accelerating the 
metabolic processes generally and proteid metabolism in par- 
ticular, while fats have the reverse effect; hence fat in the diet 
renders a less quantity of proteid sufficient. Gelatine seems to 
act when mixed with proteid food either like an additional 
quantity of proteid, or possibly like fat, at all events under such 
circumstances less proteid suffices. 
These facts have a bearing not only on health but on econ- 
omy, in the expenditure for food. 
Salts hold a very important place in every diet, though 
their exact influence is in great part unknown. The heat of 
the body is the resultant of all the metabolic processes of the 
organism, especially the oxidative ones. Certain food-stuffs 
have greater potential capacity for heat formation than others; 
but, finally, the result depends on whether the organism can 
best utilize one or the other. 
A certain body temperature, varying only within narrow 
limits, is maintained, partly by regulation of the supply and 
partly by the regulation of the loss. 
Both these are, in health, under the direction.of the nervous 
system, and both are co-ordinated by the same. Loss is chiefly 
through the skin and lungs; gain chiefly through the organs 
of most active metabolism, as the muscles and glands. 
Vaso-motor effects play a great part in the escape of heat. 
Animals may be divided into poikilothermers and homoio- 
thermers, or cold-blooded and warm-blooded animals, accord- 
ing as their body heat varies with or is independent of the ex- 
ternal changes of temperature. All the facts go to show that 
in mammals the processes of the body (metabolism) can con- 
tinue only within a slight range of variations in temperature, 
though the upward limit is narrower than the downward. 
Upon the whole, the evidence justifies the conclusion that 
the nervous system is concerned in all the metabolic processes 
of the body in mammals including man, and that, as we descend 
the scale, the dominion of the nervous system becomes less till 
we reach a point when protoplasm goes through the whole 
cycle of its changes by virtue of its own properties uninfluenced 
by any modification of itself in the form of.a nervous system. 
