oundly affected, consciousness may be lost, and the patient falls
into a comatose condition, or delirium and convulsions may set in. All
these changes can be watched in any patient suffering from an acute
fever. The lower limit of temperature that man can endure depends on
many things, but no one can survive a temperature of 45 deg. C. (113 deg. F.)
or above for very long. Mammalian muscle becomes rigid with heat rigor
at about 50 deg. C., and obviously should this temperature be reached the
sudden rigidity of the whole body would render life impossible. H.M.
Vernon has recently done work on the death temperature and paralysis
temperature (temperature of heat rigor) of various animals. He found
that animals of the same class of the animal kingdom showed very
similar temperature values, those from the Amphibia examined being
38.5 deg. C., Fishes 39 deg., Reptilia 45 deg., and various Molluscs 46 deg.. Also
in the case of Pelagic animals he showed a relation between death
temperature and the quantity of solid constituents of the body,
_Cestus_ having lowest death temperature and least amount of solids in
its body. But in the higher animals his experiments tend to show
that there is greater variation in both the chemical and physical
characters of the protoplasm, and hence greater variation in the
extreme temperature compatible with life.

_Regulation of Temperature._--The heat of the body is generated by the
chemical changes--those of oxidation--undergone not by any particular
substance or in any one place, but by the tissues at large. Wherever
destructive metabolism (katabolism) is going on, heat is being set
free. When a muscle does work it also gives rise to heat, and if
this is estimated it can be shown that the muscles alone during their
contractions provide far more heat than the whole amount given out
by the body. Also it must be remembered that the heart--also a
muscle,--never resting, does in the 24 hours no inconsiderable amount
of work, and hence must give rise to no inconsiderable amount of heat.
From this it is clear that the larger proportion of total heat of
the body is supplied by the muscles. These are essentially the
"thermogenic tissues." Next to the muscles as heat generators come the
various secretory glands, especially the liver, which appears never to
rest in this respect. The brain also must be a source of heat, since
its temperature is higher than that of the arterial blood with which
it is supp