It is clear that there is in man a power of adapting himself to very varied conditions.

This is to some extent due to his foresight, to his care, and to the power he has over nature and the animal and vegetable world.

Does he winter in the regions of eternal ice? he takes with him coal and the means of kindling fire; he surrounds himself as far as possible with an artificial atmosphere; and when he leaves that for the open air, he clothes himself with the skins of animals, which he has prepared for his comfort.

Does he reside amidst fiery heat? he surrounds himself with cooling zephyrs, while the play of fountains, breezes forced through wet mats, and punkahs driven by the natives of the climate, tend to make the atmosphere bearable.

In these respects, neither animals nor plants resemble us. The starving monkey cannot light a fire, nor can a rose tree put on a great coat for winter. The sole provision nature has given to these is, that the tree sheds the leaves which the frost would kill, and exposes its trunk and branches alone to the cold; while the animal is simply provided with an extra growth of fur to meet the inclemency of the winter wind.

But there are circumstances in which man's foresight avails him little. When pestilence invades the land there is no escaping it by surrounding himself with a pure atmosphere. The poison, free as the air, is with him constantly—yet he does not succumb to its influence.

True it is, that even here science can to some extent control the march of death, and bridle seemingly the irresistible career of the invisible Azrael. But it could not do so unless the constitution of man was so framed, as to be able to tolerate the presence of noxious influences.

That man has this power few would deny, but there are not many who have an idea of its extent.

We have read of individuals exposing themselves to the

heat of a fiery furnace, remaining in it till beefsteaks were cooked at their sides, and coming out of the ordeal with scarcely a mark of anything unusual having occurred. And we have read of children who have existed for years in our own country, in a state of perfect nudity; and we believe the

statements.

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But if we were told that one man could take, with apparent benefit, a drug which would kill another, we should regard the thing as too absurd to be worth a thought. Yet it is indeed literally true, that what is one man's meat is another man's poison," and that one individual can exist and be in health, in an atmosphere which would kill another. This immunity is brought about by a gradual change of circumstances, and we cannot demonstrate the importance of this consideration better than by quoting some experiments of Claude Bernard, which I have extracted from Lewes' "Physiology of Common Life."

"A sparrow," he says, "left in a bell glass to breathe over and over again the same air, will live in it for upwards of three hours, but at the close of the second hour, when there is consequently still sufficient air to permit this sparrow's breathing it for more than an hour longer; if a fresh and vigorous sparrow be introduced, it will expire almost immediately. The air which would suffice for the respiration of one sparrow suffocates another. Nay, more, if the sparrow be taken from the glass at the close of the third hour, when very feeble, it may be restored to activity, and no sooner has it recovered sufficient vigour to fly about again, than if once more introduced into the atmosphere from which it was taken it will perish immediately. Another experiment points to a similar result. A sparrow is confined in a bell glass, and at the end of about an hour and-a-half it is still active although obviously suffering, if at this time a second sparrow is introduced, in about ten minutes it will be found that the new

E

comer is dead, while the original occupant hops about cheerily and flies about the lecture room as soon as liberated."

After these experiments, Mr. Lewes makes some remarks upon the explanation of the phenomena, with which I do not agree, but which I will not stop to discuss, proceeding rather to some farther experiments illustrative of my meaning.

One bird," he remarks, "will live in the bell glass for three hours, but two birds of the same species, age and size, will not live one hour-and-a-half, as might be supposed, but only one hour-and-a-quarter.-Conversely, the bird which will live only one hour in a pint of air, will live three hours in two pints."

We may next quote his account of two young Frenchwomen who were in a room heated by a coke stove. One of them was suffocated and fell sensless to the ground, the other, who was in bed suffering from typhoid fever, resisted the poisonous influence of the atmosphere, so as to be able to scream till assistance came. They were both rescued, but the healthy girl, who had succumbed to the noxious air, was found to have a paralysis of the left arm, which lasted more than six months.

From the first experiments, we learn that a bird has such a power of adaptability to altered circumstances, that by gradually being exposed to deterioration of the air it breathes, it can live in an atmosphere which would destroy another bird if suddenly exposed to it.

The last of his observations does not militate against this. The girl with typhoid fever has had her system slowly accustomed to the presence of an unusual quantity of carbonic acid in her blood from the rapid waste of tissue: she is much in the same position as the half-poisoned bird, and can bear a larger dose of the asphyxiating agent than the one who comes fresh to it.

With these experiments as a starting point, let us endeavour to find out other facts which bring us to a similar conclusion.

Continuing with the lower animals, we turn our eyes from the air to the water. There we find two distinct sets of creatures-the inhabitants of salt water and those of fresh. Experience tells us that if we place these suddenly into their opposite conditions they die immediately. Thus, Forbes in speaking of some star fish, says that the most effectual mode of killing marine animals, so as to preserve their appearance, is to dip them instantly into fresh water.

This seems to prove that salt water fish cannot live in fresh, yet daily experience disproves this. Who is not familiar with the fact that the salmon leaves its lakes and rivers, and takes itself to the sea, as if it were its native element, and after awhile returns, a bigger fish, up to its original haunts in the fresh water. In every tidal river, too, vast numbers of marine animals are exposed alternately to fresh and salt

water.

Not only so, but we find occasionally in pools near the sea, a large number of shrimps and prawns, although the water is perfectly fresh. Thus, last summer I obtained an extensive haul of prawns from shallow pools on the north side of the Great Float-once Wallasey Pool-and I have yet the spectacle of the same species existing side by side in my fresh water and salt aquarium. It may fairly be assumed, that these pools were once saline, and that they have gradually become fresh by the soaking into the earth of the saline solution, and its gradual replacement by rain water.

To satisfy myself of the truth of this, I placed a minnow in salt water, and found that it died in ten minutes.

On mixing salt and fresh water in equal parts, I found that another minnow lived an hour. With two parts of fresh and one of salt, another minnow lived three hours. With three parts fresh to one of salt, another minnow lived for eight hours, and I then replaced it in my fresh water tank.

The converse of my experiments, i.e. the placing salt water

animals in fresh, was abortive, as the prawns escaped by leaping out of the basin during my absence.

I noticed that the minnows which I placed in the salt water, sank to the bottom of the fresh water tank when I replaced them in it to ascertain whether they would revive.

I do not know how far we may use the facts in illustration, but it is at least interesting to know that the fish and prawns in the Mammoth Cave, at Kentucky, which are found in pools not now connected with the interior river, have no eyes, and that horses sent down young to work in mines, soon have cataract the creatures not wanting the eye for use it becomes useless. We are all of us familiar with the ease with which a dog or cat-both carnivorous animals-adapt themselves to a purely vegetable diet; and I remember reading of a colony of dogs in a certain island, where they had been left accidentally, by ships touching there for turtle, which had learned to subsist altogether upon turtles' eggs and salt water.

We may now proceed to man, and the last anecdote will help us to our first illustration. We ask if dogs can live on sea water for drink, why cannot man? The first answer I met with to this question was in one of the reports from an Australian surveying ship, the captain of H.M.S. "Beagle," stating that the natives of the country about the Gulf of Carpentaria, had learned to drink salt water almost habitually, in consequence of the great scarcity of fresh. And in a work on shipwrecks which I consulted for another purpose, I found that one narrator describes having drunk a hearty draught of sea water while suffering from the pangs of thirst, finding himself greatly refreshed thereby; though he was subsequently purged. It is commonly stated that salt water produces madness; but as this occurs quite independently of drinking this fluid, and is a common accompaniment of starvation, we may look upon the madness so often following draughts of sea water as a coincidence rather than as effect and cause.