LXIX
working with 2 pistons. Steamers work also with 2 pistons,
but they have only a low pressure-engine. 352.
For the purpose of safety, locomotives are farther fur
nished with the safety-valve, the manometer (§ 86) and the
whistle. 353.
§ 173. By the conjoint co-operation of ebullition and con
densation (liquefaction) Distillation takes place, an operation
by which either volatile liquids and substances in solution or two
fluids of different volatility may be separated from each other.
344.
§ 174. 4) Animal Heat. The observations of John Davy
led to the following interesting facts.
1) The blood-heat of men is between 35.8° and 38.9°°C
and is not much influenced by age, food and climate.
2) For mammalia it is between 37.2° and 39.7°°C.
3) For birds it is between 37.2°° and 43.3°°C.
4) The temperature of warm-blooded animals is indepen
dent of the surrounding medium, for cold-blooded animals it is
almost the same with the medium, in which they live. Hence
the organism of warm-blooded animals must either produce heat
(by the combination of Oxygen and Carbon) or heat will be given
out.—People in the north eat more (especially carbonic sub
stances) than people living in hot climates; we eat more in winter
than in summer; after exercise we feel warm and hungry; by too
much exercise we grow lean; birds have more exercise than
mammalia, and these more than amphibious animals; hence birds
have the warmest blood and consume comparatively the greatest
quantity of food; animals sleeping in winter breathe very slowly,
their pulsation is languid and weak, their skin is cold and they
are not fleshy.
The refrigeration of the body is effected by evaporation on
