an external one. The carious portion of a tooth shows its vitality by its increased sensitiveness. In some cases the enamel, to all appearance perfectly sound, is very sensitive to the touch, indicating life in the hardest substances in the human economy. In order to keep any tissue in a healthful state it is necessary that its vital properties remain undisturbed; whenever this is So, and nutrition is diminished, morbid action commences, and we have a tissue showing the different degrees of vital energy, inflammation, granulation, suppuration and death of the part, each degree showing an action less perfect than its preceding one until the part becomes extinct.

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No satisfactory reason for caries attacking one tooth sooner than another has ever been given, beyond this: In the lower jaw the molars are more liable to the disease than the incisors, from the saliva lodging around the front teeth in larger quantities, and wherever the saliva lodges to the greatest extent, we find the largest deposits of "tartar," and strange to say, wherever that is found in greatest quantities, decay is found to be most rare, whether it is because of the extreme alkaline reaction of the saliva neutralizing the action of any acid which might aid decay, has not been demonstrated, but it is very likely to be the case.

The dentist is gradually and surely working his way to a more distinguished position every year, and now that he is called upon in consultation by the physician, he ought to be recognized as a professional brother, and not looked upon by the medical man as simply a practitioner of a mechanical art, especially when he holds a diploma of medicine and surgery. The physician can find plenty of work for the dentist if he is so inclined, and assist a noble profession which is plodding away to make new discoveries for the abatement of disease in his specialty of medicine and surgery.

SELECTIONS.

SPONGES.

The animal known as the sponge is a mere mass of fleshlike substance known as sarcode. If we examine a piece of sponge with a high magnifying power, soon after it has been taken out of the water, we find it to be covered with minute living objects, which have motion, are flesh-like, and supported by the structure popularly known as "sponge." The sponge of commerce is the skeleton of these minute animals. The almost innumerable animals that adhere to a sponge when taken out of water are called a colony. They have sprung from a common parentage, and secrete and use a common skeleton. Each particle or animal in this colony presents the appearance of an Amœba; but unlike the Amœbæ, they are grouped into colonies and secrete a common framework upon which they live. Some have the power to emit pseudopodia, others appear to be destitute of that power, but have cilia, by which motion is effected. These animals are mostly marine; there are, however, varieties of fresh-water sponges. sponge of commerce has a texture like the horn of an ox, and is therefore called corneous or horny. The skeletons of some other varieties are flinty or siliceous, while a few varieties have calcareous skeletons. The common sponge, so much in use, is obtained from the Grecian Archipelago, Mediterranean Sea, and the Bahama Islands. The organic action of the sponge consists in establishing a current of water through every portion of it; by this means each member of the colony can obtain its nourishment. The current of water passes into the sponge by the small pores on the sides, and passes out by the large ones at the top. This constant action of the water is caused by vibrations of the cilia.

The

The sponge has maintained a commercial interest and value for a period of three thousand years. Aristotle, Pliny, and several other ancient writers describe fully its nature and uses as they understood it at that time. They used it as an adjunct to the toilet, and in some of the arts of their day. Both Greeks and Romans used it extensively in bathing, in their sandals as a protection to the soles of their feet, and for medical purposes

One of the most interesting and able descriptions of the modern methods adopted for procuring or fishing for sponges, is that given by Capt. Spratt, whose personal observations were made during his travels in Crete.

He says: 66 The east coast of Crete is noted for the quantity and very fine quality of the sponges which grow in its waters, and it is in consequence annually frequented by from

fifty to one hundred boats, with seven or eight sponge divers in each, who are chiefly from the islands of Calymus, or Khalki; and they frequently visited the northeast coast during our stay there (Symi), and excited much interest among us in their occupation. Of the many varied ways by which man labors to procure his bread, there is none, perhaps, so interesting and extraordinary as that of the sponge-diver; and when the luxurious fair use the sponge at their toilet, or the gentleman at his morning ablutions and bath, little do they know or think of the hard and peculiar trials and exertions some fellowcreature has gone through before he was enabled to procure for their gratification this valuable and peculiar marine production. And as little, perhaps, have they troubled themselves with the discussion that has arisen among philosophers since the days of Aristotle, as to whether the sponge is an animal or a vegetable. Its now well-ascertained but fitful circulation of

the sea-water through its pores seems at length to have led many savants of natural history to conclude that it is really an animal. Yet this fact is all that can be advanced, viz.: That it has a spasmodic inspiration and rejection of sea-water, and, except for being covered with a slimy, viscous coating, of a bluish black color above, and dirty white beneath, the sponge is the same shape and size when cleansed and fit for use as when living, the mode of cleansing it being simply to squeeze and wash the sponge two or three times in the sea, and dry it in the sun for a few hours, until all gelatinous matter is extracted from it.

"At the commencement of the diving season, the divers suffer much, and cannot easily dive at greater depths than twelve or fifteen fathoms, for a few days; the eyes, nose and ears then bleed freely under the pressure and consequent congestion of the vessels.

"The sponge fishing is chiefly carried on in neatly rigged but small caiques, or half-decked boats, from eight to ten tons' burden, that contain from seven to nine men in each, and fine models, that seem to have been originated from the famed yacht, the America. They go to work in companies of half a dozen to twenty or thirty boats, for mutual support and protection, and when the weather is favorable, and they are in working condition, each diver will dive fifteen and even twenty times a day in as many fathoms.

"They are obliged to be particular in their diet during the diving season, making no meal until evening, and sustaining their strength by an occasional pipe and a small cup of coffee once or twice during the day.

"It is to behold one of the most interesting sights possible to be in the midst of a fleet of these sponge-boats when the men are at work on their fishing-grounds, for they are like a flight of mosquitoes, or rather of butterflies, flitting from flower to flower, as they move from one spot to another, anchoring for a few minutes only, whilst a few dives are made, then hoisting their numerous well-handled sails to shift a few yards farther in the direction desired, and then anchoring again and diving, as long as the weather is favorable, and sponges are procurable. The same ground is thus often worked over and

over year after year; but they say that a rest of two or three years is necessary to insure a good crop of full grown sponges upon the same spot.

"In a few minutes the whole party were actively diving there; and the ground being new to them, they made a great harvest in a few hours. Being exposed so much to the sun whilst diving, they look when stripped, a different race of men from the Greeks in general, in consequence of the bright copper-color of their skins, and their lean figures. The mode of i operation preparatory to a dive is very peculiar and interesting. The diver whose turn it is takes his seat on the deck of the vessel at either the bow or stern and placing by his side a large flat slab of marble weighing about twenty-five pounds, to which is attached a rope of the proper length and thickness (13 in), he then strips, and is left by his companions to prepare himself. This seems to consist in devoting a certain time to clearing the passages of his lungs by expectoration, and highly inflating them afterward, thus oxidizing his blood very highly by a repetition of deep inspirations. The operation lasts from five to ten minutes or more, according to the depth; and during it the operator is never interfered with by his companions, and seldom speaks or is spoken to; he is simply watched by two of them at a little distance, and they never venture to urge him or to distract him in any way during the process. It seems to a spectator as if the diver was going through a sort of mysterious ceremony or incantation. When, from some sensation known only to himself, after these repeated longdrawn and heavy inspirations, he deems the fitting moment to have arrived, he seizes the slab of marble, and after crossing himself and uttering a prayer, he plunges with it like a returning dolphin into the sea, and rapidly decends. The stone is always held during the descent directly in front of the head, at arms' length, and so as to offer as litttle resistance as possible; and by varying its inclination, it acts likewise as a rudder, causing the descent to be more or less vertical, as desired by the diver.

"As soon as he reaches the bottom he places the stone under his arm to keep himself down, and then walks about upon the rock or crawls under its ledges, stuffing the sponges into