HEAT AND LIFE. 153 
agents. The former is a poison of the muscular fibre, the lat- 
' tera poison of the blood-globules. The case is the same with 
heat as with the other elements of the cosmic medium, in 
which the animated being lives. Itinfolds the most contradic- 
tory powers, like the tender flower, spoken of by Friar Law- 
rence, in “ Romeo and Juliet,” from which may be distilled 
both safety and danger. It can by turns support health, 
heal disease, or inflict death. 
Man is, then, the weak plaything of all those silent 
forces that surround and press upon him. In vain he en- 
slaves them; he cannot escape the inflexible laws that sub- 
ject the equilibrium of life to that of the lowest physico- 
chemical conditions. He has at least the consolation of 
knowing these laws, and guiding his existence so as to 
soften their severity as far as possible. When Nature 
crushes him, she is unconscious of it, unconscious of her- 
- self: man, so small, is greater than these blind greatnesses, 
because his peculiar greatness is consciousness. The sub- 
ject we have been studying is a grand proof of this; but 
its full, imposing interest would not be understood, were 
we to end without giving the answer to the last question 
it suggests. Whence comes this heat developed by chemi- 
cal phenomena in the living system? It comes from ali- 
ments, which, in the last resort, are all drawn from plants, 
and they have borrowed it from the sun. When the vegeta- 
bles, whose combustion takes place within the animal, there 
throw off a certain amount of potential energy, as heat, 
they do but transmit it to the force which the sun has sup- 
plied them with. It is, then, a portion of solar radiation, 
stored up at first by the plant, which the animal makes 
disposable and converts to use, whether for resisting cold 
or for securing the regular play of his motive functions. 
Thus we may say, with exact truth, the sun is the inex- 
haustible source, as it is the perpetual spring, of life. From 
this point of view, science confirms the intuitions of oldest 
