When (as already stated) the air has a great capacity for mois ture, much injury will be sustained by those exposed to it, and vice versa.

Of Sick-Lists.

EVERY surgeon in the royal navy ought to keep two sick-lists (some now do); the first, containing those men's names who are totally incapable of performing any kind of duty, called the Sicklist; and, in the second, or Convalescing-list, those men's names are to be entered, who are in a state of progressive improvement from disease to full health; those also who have recently been under the influence of mercury, and those who have a disposition to pulmonary and hepatic affections (although they may be free from complaint at the time), are to be considered on this list, at least, during washing of decks.

All convalescing patients should only receive half allowance of grog, and this ought to be considered the sine qua non of that list, as it will have a beneficial tendency two ways; first, inasmuch as it will be sufficient for the patient's present state of health, and secondly, the high regard he generally has for it as a whole, will prevent him hanging on the surgeon's hands.

By following the above regulations, we should have a large convalescing-list, it is true; but then the sick-list would be proportionately kept down, as well as so frequent recurrence of acute disease.

OF

DRY ROT IN SHIPS.

Water re-train'd gives birth
To grass and plants, and thickens into earth.

PRIOR.

THE following observations on Dry Rot in Ships, will be considered, by many, as going out of my department; but, perhaps, I may be excused, when it is recollected, that a man-ofwar in a rapid consumption, is not only a melancholy spectacle in itself, but is rendered doubly so, in associating this national loss with a conviction that a ship's crew cannot remain long in a healthy state, when the martial walls of their habitation are quickly mouldering into dust. Moreover, the study of the laws which regulate heat and cold, moisture and aridity (the chief agents of

destruction), are closely linked with the duties of a professional man, and the growth and dissolution of all organized bodies ought to be familiar to him. Besides, the means hereafter to be pointed out for the preservation of His Majesty's ships, will also have a salutary tendency on the health of our seamen, and, on that account, have a double claim to our attention.

Notwithstanding that apparently endless variety which we observe in the vegetable kingdom, it appears, on analysis, that Nature has employed only three simple substances, oxygen, hydrogen, and carbon, in the formation of all the gradations of vegetable productions, from the majestic oak, to the dunghill mushroom.1

And, what is equally wonderful, the natural food of the fifty thousand plants already known, is as simple and uniform as their component parts: they all require atmospheric air and water only, with the addition of light and caloric to produce vegetation.2

Mr. Parkes observes, that all living vegetables have the power of decomposing water, and combining, in different proportions, the hydrogen of the water with the carbon of the soil, as well as that of the carbonic acid of the atmosphere, to form the numberless productions of vegetable nature.

It is delightful to trace the chain of connexion between life and death in vegetables, and contemplate on the important offices which water has to perform, during the growth and dissolution of the vegetable kingdom.

Death is the common consequence of all life, and, during that continual decomposition of one generation of plants after another, which takes place in every part of the terrestrial globe, a great quantity of carbonic acid is liberated in union with hydrogen, by which our atmosphere would soon have become contaminated, had not some means been provided for its renovation.

1 Some plants are said to yield, also, small traces of nitrogen, silex, and lime, &c. but these substances have undoubtedly been taken up by the

roots.

2 When we attempt to follow Nature farther, and consider the endless variety there must be in the vessels and secreting organs of plants, in order to endow them with the power of producing that countless number of fruits, oils, resins, wax, sugar, &c. which we observe in Nature; and when we remember, that trees of every description, from the cedar to the shrub, and plants, from those of the most sensitive kind within the Tropics, to the most hardy evergreen in our own regions and herbs, of every shade of color and quality, the most delicious, as well as those of the most poisonous nature, are all formed from the same simple substances (though combined in different proportions); we arrive at the ne plus ultra of human understanding, and are compelled to stop and wonder that such different products should be heated by one sun, fed by the same common nutriment, and grow in the same medium.

་

Living vegetables are the agents which have been employed by Nature for protecting us against the effluvia arising from dead ones, and clearing the atmosphere of the carbonic acid thrown off by animal respiration. For, by making what is noxious to animals, the natural food of vegetables, this most important office has been fulfilled.

Again, during the life of a vegetable, water is put under contribution for a large portion of its support, and after its death, water and heat hasten its dissolution, and set its elementary parts at liberty to enter into new combinations. And, in this manner, the elementary particles of all animated nature (whether in life or after death) are never suffered to be at rest; but perform their offices in the vegetable or animal to which they belong, only for a limited time, and after death, are again destined to occupy another place in the great circle of composition and decomposition.

But, a propos, it appears by observation, as well as by every information I have been able to procure, that the alternate changes from heat to moisture, and again from moisture to aridity, are the most favorable circumstances for hastening the destruction of timber.

The modus operandi, I think, may be explained in the following way. Caloric has the power of expanding nearly all bodies with which it unites, by insinuating itself among their particles ; and, during its operation on timber, the pores of the wood become dilated, by which means, moisture or rain is more completely admitted into its texture; and, after rain, the atmosphere will generally be found to have the greatest capacity for moisture, consequently, the evaporation from the woody fibre will then be most abundant, and, by a continuation of such vicissitudes, the decay of wood is greatly accelerated.

In this country, there seem to be only two modes by which wood may be preserved from decay, for a very long period of time: the first, by expelling the natural sap and humidity from wood before it is used, and keeping it continually dry afterwards; and, the second, by totally excluding atmospheric air under a low range of temperature, and the intervention of some dense substance.

Thousands of examples of the first kind of preservation are to be met with in old houses, where fires have been constantly kept. In such houses, even those species of wood, which, under the usual changes from aridity to moisture, and again from moisture to heat, run most rapidly to decay, are preserved for a great length of time.

Clay, water, cast iron, and some saline substances, excepted.

The second mode of preserving timber, by the total exclusion of atmospheric air, &c. is fully proved by the trunks of large firtrees being found, in many places in Scotland, several feet deep in moss, in so high a state of preservation, that the wood is frequently split by the country people and used as a kind of rush-light.1

In certain climates, there are still other means of preventing the elementary substances of animal and vegetable bodies taking their primitive forms, viz. through the medium of eternal frost, as is proved by large quadrupeds having been recently found incased in ice, in Siberia; and, secondly, by excessive heat, providing there is little or no humidity in the air, as is sometimes the case in Africa. But, as neither of these means of preserving bodies can be reduced to any practical utility in this country, it is useless to follow them farther.

In Great Britain, the woods which resist the powers of the destructive agents longest, are those which are of the greatest specific gravity, and closest texture, as the oak, for example; while the most porous, and, consequently, that of the least gravity, falls the easiest prey to destruction.

These considerations naturally led me to inquire, what is the cause or causes of dry rot in ships, in order that we may be enabled to guard against it?

:

The answer to this most important question is involved in considerable difficulty, owing to the different circumstances under which it is said to have taken place, and from the great diversity of opinion there exists amongst men on the subject.

Its cause has been attempted to be traced to a vegetable substance, to moisture, insects, impure air, putrescent juices of timber, and to the vegetable juices of timber.

It would be departing from my original intention, to follow, in an Essay, the different individuals through their various opinions

'The remains of those fine trees afford us a miserable picture of the degenerated state of our climate, probably owing to the rapid growth and insidious advances of that vegetable substance, moss.

2 "An elephant was recently found by M. Adams, near the mouth of the Lena (a river in Siberia), the flesh of which was still in so high preservation, that it was eaten by dogs." It is certain, nothing but the eternal frost in those regions could have arrested the putrefactive process in so large a quadruped, for so many centuries.

3 "We observed (says Captain Lyon, in his Travels in Africa) many skeletons of animals which had died on the desert, and occasionally the grave of some human being; all these bodies were so dried by the extreme heat of the sun, that putrefaction did not appear to have taken place after death. In recently expired animals I could not perceive the least offensive smell. Such was the dryness of the air, that the horse-tail, in beating off the flies, the blanket, and other clothing, emitted electric sparks, and crackled on being rubbed."

on this subject. But I am not inclined to impute the decay of timber to any one of those causes, abstractedly considered, but to an alternate action of certain destructive agents, to be hereafter mentioned.

Owing to dry rot being accompanied by the vegetation of fungi, some individuals have been induced to consider this as its chief cause, but, I trust, I shall be able to show, that it is only a link in the chain of causes, or rather a consequence of a certain state of the ship's timbers.

Linnæus has placed the order of the vegetable substance which accompanies dry rot, under the 24th Class (Cryptogamia), and in the 4th Order of that Class: but Dr. Smith has added a 5th Order, in which he places fungi.'

Those individuals, who assert that vegetation takes place, sui generis, from the juices of the timber, have been forced to this conclusion, from not being able to account for the universal diffusion of the seeds of fungi in any other way. But it is well known to naturalists and botanists, that the seeds of the mushroom may be disseminated by the wind, like the pollen, or poussiére séminale, of many other plants; or they may be conveyed from the forest to the dock-yard, and again, from the yard on board a ship, by adhering to the timbers, provisions, stores, &c. and there remain in a quiescent state, until called into vegetable existence, by favorable circumstances, viz. the united influence of heat, atmospheric air, and humidity.

It has already been stated in this Essay, that the decomposition of vegetable and animal bodies is greatly retarded by any of the three following circumstances; 1st, the total exclusion of atmospheric air; 2dly, great aridity of the aerial fluid; 3dly, the eternal cold of a deep flow-moss and that of the arctic circle- the most powerful antiseptics with which we are acquainted.

It appears, therefore, from the above data, that the abstraction

This Order is determined by the plant "having no leaves, and the fructification is in a fleshy substance."

The vegetable nature of this order of plants was long doubted by some naturalists, who were disposed to ascribe to them an animal origin; but the labors of Dryander, Schaeffer, and Hedwig, have shown that they possess a vegetable character, by detecting their seeds, and explaining the parts of fructification.

In the Synopsis Methodica Fungorum of Persoon, the order of mushrooms is divided into such as produce their seeds internally, or in vessels, and such as have them exposed or imbedded in an appropriate membrane. Miller's Guide to Botany, p. 181.

2

L'erigeron du Canada, cultivé d'abord au Jardin des Plantes de Paris, s'est disséminé dans toute la France, a l'aide d'une aigrette soyeuse.Nouveaux Elémens de Botanique.