carried off by the evaporation of moisture was made sensible in some especial manner, by condensation of vapour. When the moisture which condenses on the walls and windows of a room in which large numbers of persons are assembled, is examined, it is found to be impregnated with animal matter.

In the example of the heated saline solutions, aqueous vapour, with its associated effluvium issuing from the hot liquid, is immediately condensed by the colder air, and hence the readiness with which the presence of the effluvium is at that moment detected.

Evaporation takes place from every part of the earth's surface, and the rate or quantity of the aqueous vapour disengaged is in proportion to the temperature. When the ground is hot and dry, evaporation, upon the first fall of rain, is prodigious.

From the instances which have just been stated, we must conclude, that terrestrial miasms are diffused through the atmosphere in combination with the vapour exhaled by evaporation; and that quantity or potency increases in proportion as the temperature of the surfaces from which they arise increases. The miasm is dissolved by the vapour, and vapour is dissolved by the air. These are effects of the sun's rays.

The researches of Leslie, Romford, and others, have shown that different bodies have different powers of radiating caloric, and that the nature of the surface has an important influence over the process. This produces corresponding variations in the rate of cooling; those surfaces which radiate heat most rapidly becoming cold much the soonest.

When the sun descends below the horizon, every portion of the earth's surface cools by radiation; and a reduction in the temperature of the superincumbent atmosphere necessarily ensues. But, as this radiating property is very different in different surfaces, and in different situations, so great variations are occasioned in contiguous places, not only in the temperature of the air, but also in the amount of condensation of vapour; more mist, more fog, or dew, appearing where radiation is greatest. These are the effects of the night

season.

Dr. Wells frequently observed the temperature of a grass meadow at night to be several degrees below that of the air some feet above it; and thermometers, placed in different situations upon the ground, were found to mark very different temperatures, the greatest amount of dew appearing where the cold was greatest. On clear and still nights, a difference of thirty degrees Fahr. has been noticed between the temperature of good radiating surfaces and that of the air some height above them. More frequently the ground has been observed ten degrees colder than the air twenty or thirty feet above it and it is thus that the leaves of trees have been found quite dry when the -grass of an adjacent meadow is loaded with dew. "I had often smiled," says Dr. Wells, "in the pride of half knowledge, at the

means frequently employed by gardeners to protect tender plants from cold, as it appeared to me impossible that a thin mat, or any such flimsy substance, could prevent them from attaining the temperature of the atmosphere, by which alone I thought them liable to be injured; but when I learnt that bodies on the surface of the earth become often colder than the air, by radiating their heat to the heavens, I perceived immediately a just reason for the practice which I had before deemed useless. Being desirous, however, of acquiring some precise information on this subject, I fixed perpendicularly, in the earth of a grass-plat, four small sticks, and over their upper extremities, which were six inches above the grass, I drew tightly a very thin cambric handkerchief. In this disposition of things, therefore, nothing existed to prevent the free passage of air from the exposed grass to that which was sheltered, except the four small sticks; and there was nothing to radiate downwards to the latter grass, except the cambric handkerchief. The sheltered grass, however, was found five degrees Fahr., or more, warmer than the unsheltered. One night the fully exposed grass was eleven degrees colder than the air; but the sheltered grass was only three degrees colder." A canopy of clouds, walls, buildings, or any other shelter from the aspect of the open sky, act upon the same principle, and in the same way.

The question, whether on any particular night, condensation will or will not occur, and the period that may elapse after sunset before it takes place, is determined by the relation between the temperature of the air and the temperature of the dew-point. This is constantly varying. When the interval between them is large (ten or twelve degrees), some time is required for the heat of the air to fall to the dew-point, condensation is delayed, and the air is said to be dry. On the other hand, when the interval is small (one or two degrees only), condensation occurs immediately after sunset, and the air is said to be damp, and those surfaces which radiate heat quickly become soon evident, especially should the atmosphere be free from cloud, and without wind. The banks of rivers and lakes, open plains, marshes, meadows, and low situations, are wetted with dew, or the first to be shrouded in mist or fog; and they are sensibly colder than other places. Thus it is found that the conditions under which malarious diseases arise accord with the laws of evaporation and terrestrial radiation; and we conclude, that the precipitation of vapour-mist, haze, fog, or dew-may be taken as evidence of the concentration of the poison. Condensation of vapour commences; and it appears a consequence of this, that associated miasms, left alone, begin to show their proper qualities. Not that at all times noxious effluvia pass into the air, so as to be made sensible whenever dew or fog appears; but that when they do exist, quantity is determined by heat and evaporation, and poisonous qualities brought out when the associated vapour is condensed.

The peculiar properties of many bodies disappear in combination. There is nothing, therefore, to negative the supposition that the hurtful qualities of terrestrial effluvia may appear only when their union with aqueous vapour is decomposed and the theory accounts for the comparative absence of noxious qualities in the day time. It is not more difficult to conceive the irregular and unequal dispersion of hurtful exhalations over limited spots or tracts of country, occasioned by terrestrial radiation, than to be convinced of similar inequalities in the distribution of clouds and fog. And this would explain the immunity afforded by elevation. Moreover, sundry phenomena in relation to diseases have been attributed to the light of the moon; but, when the moon shines, the atmosphere must be free of clouds, and a clear atmosphere is the most favourable to the specific influences of radiation.-Association Medical Journal, Jan. 20, 1854, p. 56.

6.-Case of Scarlatina produced by Inoculation. By R. BARRINGTON COOKE, Esq., Scarborough.-During the summer of 1850, I attended a child, aged seven years, an out-patient of King's College Hospital, who was suffering from an attack of scarlatina maligna, with sloughing sore throat. The child died, and on making a post-mortem examination of the body, I inflicted a small wound on the third finger of the right hand. The wound shortly after became inflamed, and suppurated, the hand and arm painful; and red lines in the course of the lymphatics, extending up the arm, showed the track of absorption of the virus; the glands in the axilla likewise became painful and enlarged. During six days, I experienced a good deal of uneasiness and pain in the limb, accompanied with some irritative fever. Towards the end of the seventh day the characteristic eruption appeared over the body, accompanied with sore throat.

The swelling and inflammation of the arm now began to subside. The attack, which was not of a severe character, ran its usual course, and in about three weeks from the commencement of the illness, I was enabled, though in a weak state, to leave town, when after a short sojourn in the country I returned to my duties as physician-accoucheur's assistant. The urine was albuminous, but no oedema supervened. Three years previous I had suffered from a slight attack of the same disorder.

In concluding, I would remark, first, that the mildness of the attack in my own case, as contrasted with that of the child, arose probably from the difference in age between the subject affording the virus and myself; our different positions with regard to air, diet, &c., and it may be, some degree of immunity from the effects of the previous attack; secondly, that the period of latency, or incubation, was more prolonged, owing, probably, to delay in the process of absorption through the

lymphatics, whereas, in Dr. Rowland's case, the virus seems to have been at once received into the venous system.-Medical Times and Gazette, Dec. 17, 1853, p. 639.

7.-On Certain Pathological States of the Blood, especially Characterizing many Dangerous Diseases, and of the Intentions and the Means by which these States are most Successfully Treated. By DR. JAMES COPLAND, F.R.S., &c.-[The following observations are the substance of a paper read before the Medical and Chirurgical Society.]

The morbid state to which the author more particularly directed attention, might be termed contaminated or vitiated according to the causes of alteration, as these causes might be external or internal in respect of the frame; external agents and influences, as well as internal vital and functional changes, might equally be the sources of this vitiation, or both might co-operate. If a cursory view of the sources whence vitiation or contamination of the blood proceeded were taken, they would be found most numerous, varied, and often associated, and that they infected or invaded the blood by one or more channels; and although manifested in every phase and grade of morbid change, yet they frequently preserved certain specific features. These morbid states of the blood might arise-First, from causes acting on the digestive canal, and the vessels proceeding from this canal; secondly, from agents taken in by respiratory action, and through the medium of the respiratory surface; thirdly, from causes acting upon any part of the external surface or any tissue or part of the frame; fourthly, from the arrest of any depurating or eliminating function, or even from the impeded or imperfect performance of such function; fifthly, from the absorption or passage of any morbid purulent secretion or excretion into the circulating mass; and, sixthly, from the conditions of vital influence, or the organic venous power endowing the heart and blood-vessels, and from the reciprocating influence exerted by the vascular system, and the hæmato-globulin circulating through the system. The author then detailed copious illustrations of the operations of the several causes of contamination passing through these channels. The effects of various kinds of food; emanations from numerous sources of pollution; air vitiated by overcrowding; absorption by an abraded, punctured, or incised wound; the passage of sanious, puriform, or other morbid matters into the circulating current; defective action in, and imperfect discharge of, the several depurating functions, so necessary to the preservation of a healthy state of the blood; and, lastly, influences or agents, extrinsic and intrinsie, which either excite or depress the organic nervous system, reacting on the vascular system, and changing the blood circulating in it. The author adverted at some length to the operation of these conditions on the blood itself, manifested by a destruction or waste of the hæmato-globulin or red

corpuscles. He was led to believe that these changes consisted-first, in a metamorphosis of the globules, or a partial vital conversion or decomposition of them; secondly, by a portion of the globules or hæmato-globulin being converted into bile; thirdly, by the epithelial cells thrown off by the several emunctories, especially the kidneys, skin, and intestinal mucous follicles, being transformed blood-globules; and, fourthly, that they are also partly expended in the elaboration of the genital secretions in both sexes. These were the chief modes or sources of waste.-Lancet, Nov. 19, 1853, p. 483.

8.-ON NITRATE OF POTASH IN RHEUMATISM.
By DR. RICHARD ROWLAND.

[Dr. Basham speaks highly of the use of nitrate of potash in rheumatism. Dr. Rowland relates thirteen cases in which it was employed, in some cases after colchicum had failed. Three drachms of the salt, dissolved in a pint of water, were taken in the twenty-four hours; but the dose varied according to the case. Dr. Rowland says:]

From a summary of these cases, it appears that the average duration of the acute symptoms after the commencement of the treatment was about eight days. In three cases the rheumatism disappeared before the seventh day. In one it was protracted to the eighteenth. But most of the patients had the complaint some days before their admission to the hospital, and sometimes it was not possible to obtain precise information as to the date of the seizure; but so far as this could be determined, the whole average period of the acute cases appeared to be about sixteen days.

Taking the results from the most unfavourable aspect, it must still be admitted that they support the opinion of the efficacy of the nitrate of potash in rheumatism. In some of the cases the relief followed its exhibition almost immediately, and the improvement was rarely delayed for any considerable period. Besides the very obvious advantage of removing a complaint so painful as rheumatism as speedily as possible, it is otherwise important to lessen its duration, and especially because it diminishes the chances of those frightful complications which may attend the disease at every stage of its course.

In no instance was there even threatening of valvular disease. The condition of the heart was carefully watched at each visit, and in all the patients it preserved its natural sounds and rhythm. This scrutiny was always repeated before each patient left the hospital, and with similar negative results. It is true that in two instances the endocardial murmur existed; but in both these patients the complication did not commence in the hospital. One had an acute attack of rheumatism, in which the nitrate was prescribed with complete success, no vestige of heart affection being present on her dismissal. But a fort