strongest animals shrink from the defiance of the dog; but he never saw the dog shrink from the defiance of any other animal.*

SECTION V.

Animals as a Source of Food for Man.

ALTHOUGH the inhabitants of very warm climates live principally and often entirely on vegetables; in the colder climates animal food usually makes a part of the daily sustenance of all who are not oppressed by poverty: and nature has not only provided amply for this want, but has afforded the easiest means of supplying it. The disposition of those animals, which afford the great bulk of the supply that is required, as the sheep, the ox, and the swine, is such, that they are not only disposed to live gregariously, but are readily brought under obedience, so as to be inoffensive either to the person or property of man: and their docility in this respect is particularly worthy of our attention, because, from the observations of M. Frederic Cuvier, (Mém. du Mus. tom. xiii. p. 419, 420,) it appears that herbivorous animals are not, as is generally supposed, naturally more mild and tractable than the carnivorous; in fact they are by nature less mild and tractable.

The flesh of all those species, which have been above mentioned, is, generally speaking, acceptable to the human palate; and is in a great measure necessary to the support of those who are habitually exposed to great exertions and fatigue: but there are many occasions on which such food could not with any convenience be obtained, even by those to

* Linnæus, in enumerating the characters of the lion, makes, by implication, a somewhat similar observation with respect to the dog. "Leo esuriens prædatur equis et aliis majoribus animalibus;-canibus coercetur." Linn. System. Gmelin, tom. i. p. 76.)

whom the expense is not a matter of any consideration. In situations, for instance, which are far removed from any town, there are very few, with the exception of the possessors of extensive landed property, who can be conveniently supplied with animal food from their own flocks and herds: and in the case of the crews of ships, which are accustomed to make long voyages, it would be utterly impossible to find room in any vessel for such a number of live animals, and still less for the food which those animals would require, as would be competent to supply the daily consumption of all on board. But in all these instances the difficulty is obviated by the preservative quality of common salt: for we know that, by the aid of salted provisions, guarded by the regular use of vegetable acids, a ship's crew may be maintained in good health for an indefinite length of time.

And then, with reference to the general question, there are almost all the herbivorous species of birds, together with the auxiliary supply of their eggs; and those numerous species both of river and of sea fish, which contribute very largely to the support of the human race, not solely by affording food, but by affording a lucrative employment to the fisherman. I omit the consideration of the turtle, the lobster, the prawn, the oyster, and a few other species; because the aggregate consumption of such kind of food is comparatively small; and those animals, as articles of food, may be considered rather as luxuries than necessaries.

Of the animals which supply us with food, the flesh or muscular fibre is that part which is most acceptable to the palate and it is worthy of consideration that the flesh of those animals, of whose living services we stand hourly in need, as the horse and the dog, are so unpalatable that we are not tempted to eat them unless in cases of dreadful necessity. Many individuals however, through poverty, are content, and some by peculiarity of taste are inclined, to feed on the lungs or liver, or other of the viscera of

animals. And modern researches and experiments have taught us that even the bones may be rendered digestible, either by the effect of long boiling under a high degree of artificial pressure, as in the apparatus called Papin's Digester, or in consequence of the removal of their earthy basis by means of any convenient acid; and we have also learnt, from similar sources, that common saw-dust, by certain chemical processes, may be made nutritious: but we may fairly argue, from the provisional care of nature, that mankind will never be generally reduced to such circuitous means of obtaining their necessary food. In the mean time we may console ourselves with the reflection, that in the event of any temporary or local difficulty, we may find a supply of food where antecedently to the researches above mentioned we should never have dreamed of looking for it. Vitruvius mentions, in speaking of the construction of garden walks, that the fragments of charcoal, which were a common substratum of such walks, had occasionally afforded a most important magazine of fuel in a protracted siege: and in such an emergency the bones of animals might continue a supply of food, after the flesh had been eaten.

SECTION VI.

Manufacture of Sal Ammoniac.

EVEN in the present abundance of animal food the refuse is not wasted; and all that is thrown aside, as unpalatable or indigestible, is subsequently collected, for the purpose of obtaining a material, very extensively employed, and of considerable value in the arts, known familiarly under the name of sal ammoniac. Perhaps in the whole circle of the arts there is scarcely any process more interesting, if all the attendant circumstances be considered, than the fabrication of this substance: and the interest principally arises from this peculiarity in the nature of

the process, that, among the numerous products which are evolved in its different stages, there is scarcely one which is not sufficiently useful to prevent the necessity of its being thrown away.

Any one, who is in the habit of walking much in the streets of London, will frequently see some halfclothed wretched individual stooping down and holding open an apron, into which he throws from time to time pieces of broken bone and other offal, which he has disengaged from the interstices of the stones that form the carriage pavement. The unsightly load thus obtained is conveyed to the sal ammoniac manufactory; and when a sufficient mass of bones has been accumulated from this and other sources, they are thrown into a caldron of water, and are boiled for the purpose of clearing them of the grease with which they are enveloped: which grease, subsequently collected from the surface of the water on which it floats, is employed in the composition of soap.

The bones thus cleaned are thrown into large retorts, surrounded by burning fuel, and submitted to the process called destructive distillation; whereby, in consequence of the application of a sufficient degree of heat, the matter of the bone is resolved into its constituent elements, from which new compounds are formed. Of these, some pass off in the state of vapour or gas, while the fixed principles remain in the retort.

Among the more remarkable products which pass off are carbonic acid gas, commonly known by the name of fixed air; and various combinations of hydrogen and carbon, forming different kinds of inflammable air; together with water holding carbonate of ammonia (salt of hartshorn) in solution; and a peculiar oil. Of these products, the fixed air and inflammable air are disregarded, and suffered to escape. The oil is employed to feed lamps placed in small chambers, the sides of which become incrusted with the smoke arising from the combustion:

which smoke being collected, becomes an article of sale under the name of lamp black; a substance of considerable importance as the basis of printing ink, &c.

It would be tedious, and uninteresting to the general reader, to describe all the intermediate steps of the process: and it is sufficient for the present purpose to state that, towards the conclusion of it, two new compounds are formed, namely muriate of ammonia and sulphate of soda: of which the sulphate of soda is separated by the process of crystallization, and is sold to the druggists under the common name of Glauber's salt; and the muriate of ammonia, (sal ammoniac,) the great object of the whole manufacture, is finally obtained in a separate state by the process called sublimation.

The form of the bones, submitted to destructive distillation in this process, is not altered; and the unvolatilized mass, remaining in the retorts, consists of the earthy and saline matter of these bones, blackened by the carbon which is evolved from their animal matter. Exposure to an open fire drives off this carbon, and leaves the bones still unaltered in form, but nearly blanched: and these bones, subsequently reduced to powder, and mixed with a sufficient quantity of water to give them the requisite degree of consistence, are formed into vessels, which are employed in the process of refining gold and silver.

It was stated that, during the destructive distillation of bone, the carbonic acid and inflammable gases are suffered to escape: but of these the latter might be employed in supplying light to gas burners; and then, out of the numerous products of the complicated process which I have been describing, the carbonic acid would be the only substance not employed for some useful purpose.