established. We may just observe, however, that the example which he offers to the contrary, of the lake Segistan in Persia, does not apply, as it is well known that the water of the Hirmand river is merely dammed up by sand, through which, after forming a lake, it percolates, and does not pass off by evaporation: but as he boldly asserts that, from positive facts, and on scientific data,' the confluence of the waters of the Tsad with the Nile of Egypt is impossible, we feel ourselves called upon to show that it is not only possible, but probable.

He says that Debod, near Syène, 250 leagues from the mouth of the Nile, has been found by barometrical observation to be 543 feet above the Mediterranean, to which it has a fall of two feet per league; that as Debod is 325 leagues from the confluence of the Bahr-el-Abiad, the latter must be 1193 feet above the level of the sea. This deduction being neither from fact nor observation, but from an absurd theory of his, that rivers run on a logarithm,' or, as he now has it, by the Rule of Three,' will, we presume, not go for much; still less his assertion that the source of the Bahr-el-Abiad is, d'après les meilleures autorités,' about 350 leagues from its confluence with the Nile. The best authorities! he knows there is not one authority, good or bad; we are only supposing the Tsad to be the source of this river, and we are ready to grant him his 350 leagues, which concession gives him, by his rule, an additional elevation of 700 feet, making the source of the Bahr-el-Abiad, or the lake, 1880 feet above the level of the Mediterranean. It is quite certain that if the Tsad be only 1200 feet above the sea, as Dr. Oudney makes it, and the confluence of the Bahr-el-Abiad with the Nile 1193 feet, as gratuitously assumed by M. Jomard, the waters of the former could never reach that point of confluence; but the fact is, we are utterly ignorant of the elevation of this point; and even that of the Tsad is but an approximation. We find it stated that, at Tripoli, the barometer was registered regularly three times a day for three months, the mean height during that period being 30. 39 inches; that about the middle of the desert it generally stood at 28. 50, and at Kouka from 28. 72 to 29 inches. Here we have some data to go upon. Taking, then, the mean of the two latter, we shall have 1340 for the approximate height of the lake, which is 140 more than Dr. Oudney has stated it to be. We are content, however, with taking the elevation at 1200; the direct distance from the lake to the confluence of the Abiad with the Nile at 1100; and from thence to the Mediterranean the same; we have then 2200 miles, with an elevation of the source equal to 1200 feet, which gives a fall of 63 inches per mile. Comparing this with that of the Amazons, which Condamine makes to be less than 7—

with the Mississippi, which Schoolcraft's data make less than 6* -with the lower part of the Ganges, which Major Rennell makes less than 5-we need not hesitate to admit the fall of the Bahr-el-Abiad and the Nile to be amply sufficient to convey the waters of the Tsad into the Mediterranean.

But to pass over the, at best uncertain, results of barometrical admeasurements, if it should be found that the country to the eastward is of the same kind as that to the westward of the lake, a fall of two or three inches per mile would be quite enough for a series of lakes and swamps to drain off the water; and the supposition that such is the fact is consistent with every information that has as yet been collected. The Bahr, now Wad, el-Ghazal, the very name of which implies the nature of the surface, and which, according to the accurate Burckhardt, is a wide extent of low ground, without any mountains,' is the first beyond the lake; then Fittre, in which by all account there is a great lake, or chain of lakes; beyond, in Dar Karka, there is said to be a great river, called Bahr-el-Freydh, or the inundating river, and beyond this a large fresh-water lake, called Wadey Hadaba; and then farther on is Dar Saley, of which Burckhardt says In the rainy season, which usually lasts two months, large inundations are formed in many places, and large and rapid rivers then flow through the country. After the waters have subsided, deep lakes remain in various places, filled with water the whole year round, and sufficiently spacious to afford a place of retreat to the hippopotami and crocodiles which abound in the country.' Then we are informed by M. Jomard, that a French gentleman, of the name of Hey, has been up the Bahr-elAbiad 180 miles, and that it there maintained the character given to it by Bruce, of being a dead-flowing river.' Putting these notices together, and considering what the Yeou is to the westward of the lake, as far as Katagum, where not a pebble is to be found on the surface, which is one flat of lake, swamp, or sand, we think we need not boggle much as to the insufficiency of the full for carrying the waters eastward of the Tsad. We must therefore adhere to the conclusion we came to in a former Article, viz. that the junction of the waters of this great lake with those of the Nile is not only possible, but extremely probable.

Schoolcraft, by an extraordinary blunder of making the dividend the divisor, gives a mean fall of two feet three inches to the Mississippi; and Jomard, who has written three pamphlets on the slopes of rivers, repeats the blunder.-See Quart. Rev. No. LVII.

The lower part of the Mississippi has no more fall than this. Major Long has calculated the head of the Illinois at 450. The length of this river to its junction with the Mississippi is 1200 miles, and of the latter from thence to the Gulph of Mexico 1200 more: the fall being 450 feet in 2400 miles, or 24 inches per mile-yet with this gentle slope its current is impelled with a velocity of more than three miles an hour.— Quar. Rev. No. LVII.

ART.

ART. XII.-A Letter to Sir Henry Halford, Bart. President of the College of Physicians, proposing a Method of inoculating the Small-por which deprives it of all its Danger, but preserves all its Power of preventing a second Attack. By R. Ferguson, M. D. Member of the College of Physicians of London and Edinburgh. 1825.

ABOUT twenty years ago, when it was proposed to purify the medical profession from quackery and ignorance by legislative enactments, the late Dr. Gregory of Edinburgh published a letter on the subject, in which he remarked that England is a free country, and the freedom which every free-born Englishman chiefly values, is the freedom of doing what is foolish and wrong, and going to the devil his own way.' This is strikingly exemplified in the present state of vaccination in Great Britain, compared with its state in other countries of Europe. In the latter, general vaccination was ordered by government; no one who had had neither cow-pox nor small-pox could be confirmed, put to school, apprenticed, or married. Small-pox inoculation was prohibited; if it appeared in any house, that house was put under quarantine; and in one territory no person with small-pox was allowed to enter it. By such means the mortality from this disease in 1818 had been prodigiously lessened. In Copenhagen, it had been reduced from 5500 during 12 years to 158 during 16 years. In Prussia, it had been reduced from 40,000 annually to less than 3000; and in Berlin in 1819 only 25 persons died of this disease. In Bavaria only 5 persons died of small-pox in eleven years, and in the principality of Anspach it was completely exterminated. In England, on the other hand,—in England, the native country of this splendid and invaluable discovery, where every man acts on these subjects as he likes, crowds of the poor go unvaccinated; they are permitted not only to imbibe the small-pox themselves, but to go abroad and scatter the venom on those whom they meet. A few years ago it broke out in Norwich, and carried off more persons in one year, than had ever been destroyed in that city by any one disease, except the plague. A similar epidemic raged at Edinburgh; and last year it destroyed within one of 1300 persons in the London bills of mortality.

Before the introduction of inoculation, the small-pox was the most loathsome and fatal disease with which Great Britain was afflicted. It killed about one out of four of those whom it attacked, and left many of the survivors with blinded eyes, scarred faces, and ruined constitutions. When, therefore, inoculation was introduced into this island, it seemed a prodigious improvement; by this simple contrivance, especially after the method

method had been improved by the Suttons, a disease which killed one out of four, was transmuted into a disease which killed only one in several hundreds. If this had been the only result, the benefit would have been unmingled, and great in a degree almost incredible, but it brought with it an evil still greater than the good; by perpetually keeping up a supply of the contagion, this disease, which had been propagated only at intervals before, was now propagated perpetually, far and wide, among those unprotected by inoculation; the annual mortality was greatly increased, and that, which all had hoped to find a blessing, turned out to be a national curse.

It is not surprizing, therefore, that when Jenner disclosed the wonderful truth, that the artificial production of a trifling and harmless disorder would impart a charmed life over which this loathsome disease should have no power, his discovery was soon hailed with enthusiasm by almost the whole medical profession. In the general exultation, its infallibility was over-rated; the advocates for vaccination affirmed that it was an infallible protection from the small-pox, and every instance of small-pox after cowpox was explained away. Such cases are now no longer to be denied. Patients have caught the small-pox who had been vaccinated by the most skilful vaccinators, even by Jenner himself, and it is generally acknowledged that out of a number of vaccinated persons, some do not resist the contagion of the small-pox.

The time has now arrived when all intemperate excitement on the subject is at an end. Vaccination has been tried on a vast scale for seven-and-twenty years, and we have a stock of experience whereon to determine (not with mathematical precision, yet with enough for the guidance of our conduct) to what extent vaccination has disappointed our expectations, and whether this disappointment is sufficient to induce us to abandon the practice altogether.

This general question resolves itself into two particular ones: 1st. What is the proportion of the vaccinated who are liable to the infection of small-pox; 2d. Do they suffer when infected as severely as those who have never been vaccinated, or is the smallpox in their case mitigated and converted into a harmless disease?

But

From the introduction of vaccination down to the present time, numerous instances have been recorded of an eruptive disease, similar to small-pox, in persons previously vaccinated. though these records afford specimens of this occurrence, they throw no light on the question of its frequency; we pass them over, therefore, and select a few instances in which the security afforded by vaccination has been tried on a large scale, and the

first which we shall notice is a small-pox epidemic* which raged in Norwich in 1819, and which has been described by Mr. Cross, a well-informed and indefatigable surgeon of that city. The small-pox had been extinct in Norwich from 1813, to June, 1818, when a country girl, travelling from Yorkshire, caught it in a market-town through which she passed, and was taken ill soon after her arrival at Norwich. This girl was the innocent cause of the death of more than 500 persons; all of whom might have been saved if there had been a small-pox quarantine. For several months it crept from house to house like a spark of fire along a streak of gunpowder, but in February, 1819, it reached a charity school, a magazine of combustibles, and the explosion scattered firebrands all over the city. More than 3000 persons caught the disease; it proved fatal to 530; 43 were buried in one week, 156 in June, and 142 in July.-Now, there were in Norwich about 10,000 vaccinated persons exposed to the full rage of this very contagious and malignant small-pox. How did they stand

it?

In 42 poor families, there were 91 persons who had been vaccinated at various periods from 1798 down to the commencement of this epidemic; these persons were continually in the same room, and many in the same bed, with those suffering smallpox; of these 91 persons, only two caught the small-pox. But besides those exposed to the contagion, several hundreds of the vaccinated were inoculated with small-pox. In one out of 40 or 50 there came out a slight eruption, which lasted only four or five days. Thus it appears that the proportion of vaccinated persons who were susceptible to the contagion was rather more than two out of every hundred. But when vaccinated persons caught the small-pox, what degree of severity did this disease assume? In no instance,' says Mr. Cross, 'has regular small-pox, as far as I have been able to ascertain, been produced. In about one in 40 or 50 a spurious eruption has appeared, in some presenting a few irregular pimples, in others resembling the small-pox; but I have not learnt that the latter have ever proceeded regularly, invariably drying up in four or five days, and never taking the course of regular small-pox.' 'Full-length small-pox in those who have been vaccinated,' continues Mr. Cross, has been so rare that I have not met with a single instance either in my own practice, or in my inquiries amongst the poor.' A few such cases, how

An epidemic is a prevalent disease, whether its prevalence arises from contagion, or from an unhealthy state of the air. In our last Number, under the article Plague, we consented to restrict this word to the latter class of diseases; this had been already done by the Anti-contagionists, and we were unwilling to waste time in a dispute about words when we have so heavy an account to settle with them about facts and reasonings.