1of THE STRUCTURE AND LIFE OF BIRDS cHap, 
But they do not all centre in this, and the exact part 
of the brain from which some of them come has yet to 
be discovered. The vaso-motor nerves not only have 
local power, but by combined action can affect the 
temperature of the body generally. They lower it 
by sending a large flow of blood to the surface ; 
more heat will then be lost through radiation and con- 
duction, and in man by evaporation. Thus exercise at 
once raises and keeps down temperature—raises it by 
muscular activity which always generates heat, keeps 
it down by bringing blood tothe surface. In exposure 
to cold, the blood withdraws from the surface, and 
protects the vital organs from chill. 
It is supposed by high authorities that there are yet 
other nerves or nerve-fibres, which have more complete 
power over temperature in that they control directly 
the amount of oxidation. When a warm-blooded 
animal is dosed with the drug urari, it behaves like a 
cold-blooded creature. Ifthe nerves that arise from 
the medulla oblongata are ‘severed, the results are 
the same in kind, though not so striking. This 
cannot be due to the vaso-motor nerves, which 
only regulate the amount of blood sent along the 
arteries. 
The subject will be more intelligible, when I have 
made clear what is meant by “behaving like a cold- 
blooded animal.” For purposes of distilling, a chemist 
puts various substances in a retort and exposes them 
to heat, and the greater the heat applied the faster 
the process goes on. <A cold-blooded animal has 
been well compared to such a mixture of dead 
substances in a chemist’s retort. Heat increases and 
