[CHAPTER VI.]
EFFECTS ON ANIMAL AND VEGETABLE LIFE.
As salt is one of the principal constituents of the blood, and as it is present in the various tissues of the body, and as its ingestion is necessary for the animal economy, for the maintenance of its health, and consequently for the due development of the several organs, and the invigorating effects it exerts over their functional activity, we will now consider it in the relation it holds to animal and vegetable life.
By the great majority of land animals salt is evidently an article much relished, for in those districts where salt springs and lakes are prevalent, many quadrupeds and birds are invariably to be seen.[50] They frequent these spots in great numbers, and very seldom migrate to those districts which are deficient in salt, or, if they do, very speedily return; these animal instincts are indicative that they are aware of its bracing qualities, and experience the salubriousness of the atmosphere, which naturally is impregnated with a fair amount of salt, which has risen through the media of exhalations from the water or evaporation of the same.
In the Ruminantia the beneficial and, indeed, the salutary action of salt is remarkably observable, for it counteracts in this class of animals the deleterious effects of rainy weather, damp pasturage, and damaged fodder. It also imparts a consistency to the fat, and renders the meat more palatable and wholesome. All cattle, without an exception, thrive best if they are supplied with salt; and they will consume no small quantity. Horses will, on the average, consume daily six ounces; cows, four ounces, and will, it is said, secrete a larger quantity of milk, and of a much richer quality, than those from which salt is usually withheld. Sheep will consume half an ounce daily, and they are not affected with the rot, as is so frequently the case in low-lying marshy districts where they drink water in which there are myriads of the fluke-worm, embryonic and developed, especially after heavy rains or inundations, as, for instance, a river overflowing its banks. It is a fact which farmers and graziers should by no means lose sight of, that these worms are totally destroyed by giving sheep a certain amount of salt during moist and wet seasons, and in those localities which are generally in a state of humidity.
In marine animals common salt is a necessary constituent of their drink, and in fact it is the preserver of their life; but it is injurious, if not certain destruction, to many fresh-water fish, though some live both in the sea and fresh water—as the salmon, sturgeon, and some species of lamprey. The male salmon, on entering the mouths of rivers in order to spawn, follow the females, and fecundate the ova which they have deposited in little pools, or kinds of nests. They, therefore, are hatched in rivers. After the first year they remove to the sea, and, remaining in it for about two months to ten weeks, return to fresh water. Such is the alternate fresh and salt-water life of the salmon, showing us that some fish can live in the sea and breed in fresh water.
Reptiles and animals of an inferior class are deprived of life by the action of salt water; and such organisms as the amœba, hydra, rotifer, and others of a similar grade which we see in stagnant ponds, are speedily killed if put into water in which salt is dissolved; this is also the case with earth-worms, snails, and indeed all insects as a general rule, especially if generated by animal and vegetable decay.
Owing to the antagonism of salt to life produced by putrefaction, it is frequently rubbed into meat to prevent it from being attacked by putrescent larvæ; and even if decomposition has commenced, it arrests for a long time its further progress. We all know what an intense irritant it is to leeches, and how they immediately vomit if some salt is sprinkled upon them when they are engorged with blood.
Land shells are rapidly killed by sea-water, and so are their eggs; this fact has been demonstrated by Darwin, who says: “Their eggs, at least such as I have tried, sink into it and are killed.” From experiments performed by Baron Aucapitaine, we find the above corroborated. He placed in a box, pierced with holes, one hundred land shells belonging to ten different species, and then immersed it in sea-water for a fortnight; only twenty-seven recovered.
These experiments are conclusive, and prove that salt destroys life of an inferior grade, probably owing to the fact that, generally, it is calculated to produce results of a nature somewhat disposed to become an annoyance, or even inimical to the vitalisation of superior organisms, and tends to arrest their progress and due development. We must remember that these two experiments of Mr. Darwin and Baron Aucapitaine were with sea-water, consequently the other salts which it holds in solution (the sulphates of soda and magnesia), and the organic matter which it contains, very probably hastened the progress.