direction, but very irregular both as to space and time; — that it appeared at Madrid about three months later than in Scotland, and in Malta six weeks still later; - and that various intermediate towns and tracts of country seem to have been wholly exempted; - we cannot reasonably look to weather as a direct cause, whatever its influence in giving action or diffusion to other materials of disease.

Amongst other particular proofs to the same effect, the following may be cited as especially remarkable. The influenza of 1831 began in London about the middle of May, and continued during June and a part of July, under very hot though damp weather. While that of 1837, still more violent in degree, appeared during the first days of January at the close of a severe frost, and prevailed till towards the end of February; followed again by weather of singular severity. Again, with respect to this latter epidemic, we have the fact of its raging in England and the northern parts of Europe during the depth of winter; while its prevalence in some southern countries of Europe was extended to the latter end of May, or the beginning of June.

I may mention as another evidence of the same kind, and interesting from the remote part of the globe which furnishes it, that a severe influenza, having all the characters of the European epidemic, prevailed in Van Diemen's Land in December 1838; the season, therefore, corresponding with the month of June in our hemisphere.

Recurring to a former period, the influenza which spread over England in 1782 during April and May, had been noted in the East Indies during the latter months of 1781; had prevailed in Russia from December to February; and did not reach Italy and Spain till the autumn of 1782, three months after its prevalence in England.

It is impossible to look fairly at these circumstances, and

not to see that the known conditions of the atmosphere, as we estimate them by our instruments, are inadequate to their explanation. Perhaps the more than common prevalence of easterly winds, with a hazy atmosphere and dense fogs, during the seasons of these epidemics, are the facts most favourable to the hypothesis in question. The latter circumstance in particular has been noted at many different periods of their Occurrence. And, though correct observations are much wanting on the subject, something may be assigned to the electrical state of the air, manifestly disturbed during some of these periods, and possibly becoming in this disturbance the cause of the phenomena just noted. Still these circumstances are too partial, and too often occurring without like concomitant effects, to justify the belief that they act as direct causes of the disease. The most summary statement then of

the argument is this:

that all obvious conditions of weather being the same in a certain number of places, the disease appears in them at very different times, or in some not at all:- and secondly, that it occurs in various places, or in different years at the same place, under states of season and weather wholly opposed to each other.*

Sir G. Baker, though relating certain singularities in the winter and spring of 1762, yet is wholly opposed to the view of these being directly concerned as the cause of the epidemic. Amongst other objections to this, he states the fact that places within two miles of London were attacked much later than London itself. He remarks further, what well merits notice, that the disorder appeared in the metropolis before it was known in any other part of Britain. It began here the first week in April, in Edinburgh a month later, in some parts of the north of England not before the end of June.

Before quitting this subject, I must refer to a very valuable memoir by Dr. Black of Bolton (see Seventh Report of the British Association), on the epidemic of 1837, as it appeared in that town. This paper, besides other important statistical details, contains a meteorological register for the first three months of the year; from which, however, no especial inference can be drawn in relation to the periods or peculiarities of the disease.

Arguments of the same kind, somewhat modified, apply equally to the notion of what has been vaguely termed terrestrial influence- an undefined agency proceeding from unknown source within the earth itself. In one instance, the simultaneous appearance of a similar epidemic in the northern and southern hemispheres might seem to give sanction to such hypothesis; but this instance, as far as we know, is a single one, and cannot be placed in opposition to the many facts attesting the slow and irregular progress of the disease even through adjacent localities, under conditions apparently the most inconsistent with this idea of its origin.

I have dwelt so far in detail upon these questions, not merely from their intrinsic interest, but from the connexion with many other important points in the history of disease. Whatever the causes of influenza, it is clear that they are closely associated with conditions which operate in producing or giving greater frequency to other disorders also. It is most important to estimate the nature and extent of these connexions, and the illustrations which they mutually afford. And no disorder furnishes such information more remarkably than that of which we are now treating.

It is impossible that the relation to the Asiatic Cholera should escape notice here. notice here. Independently of some singular concurrences as to time, the question regarding dependence on atmospheric causes is so much alike for the two epidemics, that any argument admits of being directly translated from one case to the other. The symptoms are less analogous than the manner and extent of diffusion of these erratic disorders but even here there are certain resemblances in the suddenness of invasion: and the rapid or sometimes instant prostration of power which ensues. All the proofs we possess of a virus peculiar to the cholera equally apply to the epidemic influenza; and the need of such specific agent to

explain the facts is scarcely less than in the case of scarlet fever or measles, though there is no evidence of contagion here as complete as in the latter diseases.

I have already noticed the argument to this effect from the identity of the disorder at different periods of its occurrence, and in distant countries; and the force of this becomes more apparent on consideration of the various details of time and locality given above. On careful comparison of my notes during the several influenzas which have occurred since 1831, and extending the comparison to those best described of former periods, I cannot doubt that every essential character of the disorder is the same; and that there must be identity of material cause to explain this fact. It seems impossible to suppose any series of circumstances, really different, yet thus capable of producing and disseminating the same exact character of disease; and under conditions which needfully imply a continued and fresh production of the morbid cause. The near equality as to periods and duration of the disorder in each given place is a strong collateral argument; a correspondence extending even to the period which it has generally occupied in passing over the different countries of Europe. Were other argument wanting to establish identity of cause, it might be found in the remarkable sequelae of the disease, to which I shall afterwards advert.

While admitting, however, as almost necessary, a specific virus or matter of the disorder, we are scantily provided with facts to indicate its manner of generation and spread; - why it should be produced at periods so irregular as to interval ; — and the precise nature of its action on the human body. Still these difficulties are not greater than occur in the case of the contagious exanthemata; where but for the familiar view of infection (an explanation itself of recent date in some of these disorders, and which gives the aspect of more knowledge than

it really conveys) we are equally ignorant of the nature of the animal poisons concerned, or of their manner of action. That the virus, if not generated by certain conditions of atmosphere, derives activity or power of diffusion from them, must be admitted as probable; and it is under this view that states of weather may be considered to have influence, and not from changes in the obvious qualities of the air operating directly on the body. The distinction here is obvious; and best accords with the facts already noted in the history of these epidemics. It is, moreover, more satisfactory to reason than the vague phrase of an epidemic constitution of atmosphere, which can be understood only by referring to the points on which such distinction is founded. *

Without speculating on the nature of a material agent, which if existing, is yet removed from all direct research, the question may fairly be entertained, whether this disease of epidemic influenza is contagious in the ordinary sense: and also whether the virus, when received, has a period of incubation, like the infectious matter of some other diseases.

On the first of these questions, the opinions of medical men have been for the most part negative; though without much inquiry directed expressly to the subject. This is sin

* In another chapter I have stated the arguments which may be alleged for the hypothesis of animalcule life as the source of the Asiatic Cholera. It is obvious that many of these arguments, if valid, must apply equally to the epidemic influenzas now under notice. But I do not repeat them here; it being enough to state once what is still speculation without proof; and the cholera furnishing a better instance than any other on behalf of the hypothesis.

There seems sufficient evidence that, among other animals, horses and dogs at least are subject to a disorder resembling influenza, during the period of its prevalence in any given locality. The influenza of the last spring (1840), comparatively mild in its character, was attended by a general and somewhat severe epidemic among cattle, affecting particularly cows and sheep.