cold winter, there will be in the following summer acute fevers, catarrhs, and bloody discharges. With a dry and northerly spring, following a rainy and warm winter, there will be bloody discharges, ophthalmia, rheumatism, and catarrhs, fatal to old people. Abortions easily arise under these conditions, and children thus born near the spring are weak and diseased, and either grow up so or die quickly. A rainy and warm (southerly) autumn, following a dry and cold (northerly) summer, will produce in the winter pains in the head, cough, catarrhs, and consumption. A dry and cool (northerly) autumn is good for those of a moist temperament, but to others it produces ophthalmia, acute and lingering fevers, and melancholy.

Great droughts are more wholesome and less destructive than continual rains and frequent showers. Continual rains cause most diseases, as lingering fevers, diarrhoea, diseased humours, falling sickness, and apoplexy. Great droughts occasion consumption, inflammation of the eyes, rheumatism, incontinence of the urine, and bloody discharges.

Continued northerly weather braces and strengthens the body, makes it agile, freshcoloured, and quick of hearing. It restrains the bowels, increases chest-pains, and offends the eyes. Southerly seasons relax and moisten the body, dull the senses of hearing and sight, cause heaviness, vertigo, laziness, and diarrhoea.

Children and very young people have good health in the spring and the beginning of summer; old people in summer and some part of autumn; people of middle age in autumn and winter.

All diseases appear at all seasons, but some are caused and exasperated rather in one than another. In the spring, affections of the brain, falling sickness, discharges of blood, affections of the throat and chest, diseases of the skin, and rheumatism. In summer, some of the above; also burning fevers, agues, disorders of the stomach and bowels, violent sweatings, and affections of the eyes, ears, and mouth. In autumn, many summer diseases, also fevers, enlargement of the spleen, dropsies, consumption, asthma, diarrhoea, and dysentery; iliac passion, falling sickness, and brain diseases. Present Liability to Disease.-The existence of seasonal disease is well established, for from the era of Hippocrates to our day the experience of mankind has borne testimony to the variations in the prevalence of disease at various seasons of the year, and to the fact that the same kind of disease assumes a different aspect at various seasons; or, to speak more generally, in various years. We need only refer to the occurrence of the plague

in London in 1593, 1603, 1625, 1636, and 1665,* all of which received their vast development in the hot season, and to the general manifestation of cholera in our day at the same periods. The occurrence of yellow fever at the end of summer in southern climes, the prevalence of special eruptive maladies at different seasons, and the occurrence of inflammatory diseases in the cold season, are familiar illustrations of universal belief upon this subject; but as we shall hereafter give details upon this question, we shall not now discuss it further.

The foundation of seasonal disease is the varying degree of vital action proceeding within the body at the different seasons of the year.

We must admit that disease is in its principal forms an exaggeration of a natural tendency then existing in the human body-a tendency which only becomes disease when carried beyond a certain limit. Thus we find that a person of feeble habit is especially liable to disease in which exhaustion is a prominent feature, and one of plethoric habit is unusually exposed to congestive and inflammatory diseases.

We have already shown that the human system varies in its amount of vital action in a very definitive manner, the maximum being in the spring, the decline and the minimum in the summer, the minimum and the increase in the autumn, and a stationary elevation in the winter. Just in the like order is it ex. posed to an exaggeration of these tendencies. Thus, as a rule, the diseases of the end of summer are those of exhaustion, whilst those of winter and spring are known as inflammations, and those of autumn and the end of spring are marked by such conditions as result from rapid variation in the animal economy in its relation to the influence of external agents. There is also a variation in the type of disease according to the advancing tendency of the system, so that in the later part of spring, when there is the commencement of a downward tendency of the vital actions, the progressive attacks of the diseases will progressively show an asthenic type, until they at length terminate in the diseases of exhaustion infesting the summer season; whilst, on the other hand, diseases occurring at the end of summer and the early autumn progressively change their aspect from the asthenic form until they merge into the sthenic conditions of winter.

Hence there are both settled sthenic and asthenic conditions, and conditions varying in a definite direction between them, and as they are due to the amount of vital action existing (which results from the influence o

phenomena within the system; whilst the former are, so to speak, natural-for the most part flowing from natural causes-and act by adding force to the natural order of phenomena. Both are connected with season, but the latter alone can be truly regarded as seasonal, and subject to the law of cyclical change, which we are now discussing.

There are diseases which result from an arrest or lessening of the natural tendencies of the system.

Such is the character of disease which is induced by an excess of seasonal influences or in a system unusually sensitive to the ordinary degrees of seasonal influence-viz., one of exaggeration of the natural tendencies of the system; but there are other diseases arising from a contrary condition. Thus, if when the temperature is increasing, and the skin is required to be unusually active, so as to produce great dispersion of heat, some condition occurs which leads to the arrest of, or a serious diminution in, the action of the skin, the natural tendency of the system is thwarted, and the only condition compatible with health being for the time set aside, a state of disease immediately ensues. This is familiarly illustrated by a cold, the ordinary effect of undue exposure of a part of the body to a lower temperature, and also by the indulgence in such articles of food as tend to lessen the action of the skin. Or again, if during winter, when the action of the skin and the sensibility of the surface should be much reduced so as to prevent an undue waste of heat, and to pass unheeded the influence of cold, a condition be imparted which tends to maintain the skin in the normal activity of summer-as, for example, the occupation of highly-heated apartments, or the constant use of the Turkish bath-the body will be liable to the effects of too great dispersion of heat, and will certainly be more sensitive to the influence of external cold. Or finally, if with the necessity for high vital action in the winter and spring there should be deficient nutriment supplied, there will be an arrest of that condition which is natural to the body at that period of the year.

All this latter class of causes may be regarded as adventitious or accidental, and they

The constitutional peculiarities of individuals modify the effects of season.

The relation of these internal changes has already been demonstrated, but it may be well to show yet more clearly that there is a constant antagonism proceeding between those external influences and the vital actions of the system; and although the influence of the external agents will in the end draw the vital changes of the body in their train, there is not a uniform readiness to submit to their controlling power. This is commonly referred to the constitution of the individual, so that it is said that such a one "suffers much from hot weather," or he "bears hot or cold weather well," according to the peculiar tendencies of his system to aid or resist the influence of external agencies. The former illustration has been abundantly exemplified in two investigations which have been already referred to. In that conducted at the Brompton Hospital on fifteen cases of phthisis, during the increasing temperature of the month of June, there was found to be great variation in the effects of the season in the different cases, and it was ascertained beyond a doubt that those who knew from experience that they bore heat badly had an excess of all the seasonal effects. So, in like manner, when determining the amount of carbonic acid evolved daily during the year, Mr. Moul, who suffers much from heat, showed a much greater diminution in the amount of carbonic acid evolved under the influence of temperature than we evinced who bear heat well-his diminution being, as already stated, 27 per cent. at the middle of June, whilst ours was but little more than that amount at the end of August.

In this, no doubt, lies the explanation of the selection of a few victims when many persons are exposed to the same morbid conditions, for it is well known that although there may be an epidemic of influenza or an outbreak of cholera which may extend over a great city, only a small proportion of the popu lation thus exposed will be seized by it. It has always been difficult to explain this fact, and hence many theories have arisen referring to the accumulation and the transmission of the morbid influence, each of which may have some weight, but no one has been shown to

exert so general a power as to be regarded as an adequate cause of this diversity. Now, however, it having been proved that morbid influences arise under certain external conditions which, whilst they lead to variations in the vital powers of the system, have greater influence upon certain individuals than upon others, we have a ready and general explanation of the selection of such persons as the earliest victims. But, with this truth admitted, we may still need increased information as to the origin and transmission of the morbid influence, as well as to the mode by which those external agencies act which both engender these morbid agents and prepare the system for the reception of their influence.

The dangers to be apprehended in the progress of disease vary with the season.

In the maximum and minimum conditions of the system we find that causes have been long acting, and have gained power by continuance, and hence the dangers will increase as the season progresses. This we shall show to be the case in a remarkable degree in the summer season, as manifested by the progress of cholera, and in the winter season by the progress of bronchitis.

In the season of change the danger lies in the difficulty of adapting the body with its numerous functions to a new order of external phenomena, and hence the danger will be the greatest at the commencement of the period of change, and this may be well illustrated by the early severity and special cause of death from eruptive diseases at the two periods of change.

The frequency of certain diseases has a relation to the season and to the nature of the disease.

We have affirmed that the diseases of hot weather show an adynamic and those of the cold weather a dynamic type, whilst the characteristic of the spring and autumn months is that of change; and we now purpose to show that such is the actual nature of the diseases which prevail at those periods.

For this purpose we have analysed the London returns of the Registrar-General for the five non-epidemic years of 1850 to 1854, both inclusive, and have ascertained the amount of mortality which occurred from each disease in each quarter of the several years. When these results are compared with the mortality which would have occurred had the deaths been uniformly distributed over the year, we at once perceive the periods of excess or defect, and it is upon that principle that the following table has been compiled :

Smallpox Measles Scarlatina Typhus

Maximum Decreas-Minimum

and In

creasing. Minimum creasing.

Vital Changes.

1st Quarter.

2d Quarter

3d 4th Quarter. Quarter.

Maximum.

and De- ing and

15-2 17+

145

2.9

+364 + 4:0

6.9

+ 0.2

+44

46

0.5

24 14

+ 2:3 +07+ 46 + 5.0 + 5.0 + 12.9

48

19 +1.1

++++++++ |||

2.4

--

10-7 + 6.7

6415

1-7- 2.1 +1.2

3.7 - 2:33:0

2.1 - 2.0 + 0.5 +.42

It is manifest that there are inconveniences in the construction of this table, for as we have shown that certain months exhibit changes of far greater magnitude than others which are comprehended in the same quarter, the full effect cannot be shown when all are added together. This is particularly the case in the second quarter, for whilst April and May are maximum months, June is a month of marked decline. Such diseases, therefore, as depend upon a diminution in the vital powers will scarcely exhibit this characteristic when compared with the conditions of the previous maximum periods. Hence it would have been better for our purpose if the mortality from each disease could have been recorded in each month separately, but the publications of the Registrar-General do not give the required data.

Again, the mortality is not sufficient evidence of the prevalence of a disease, for whilst it embraces the question of frequency, as well as that of intensity, the former is necessarily subordinate to the latter; but here also published data fail us, and we are compelled to be content with a knowledge of the mortality alone.

All these circumstances militate against the full development of the results which we seek; and whilst the latter are very decided in the foregoing table, it may be inferred that their value is greater than the treble power.

Diseases of the alimentary canal have their maximum intensity and frequency at the period of minimum vitality.

Diarrhoea is the most marked illustration of this fact, for whilst there is a defect in each of the three other quarters, there is an excess of no less than 36 per cent. in the quarter of minimum vitality, and the extremes are so great as a defect of 15 per cent. in the maximum, and an excess of 36 per cent. in the minimum quarter. These numbers are so decided that for all practical purposes diarrhoea may be regarded as a disease solely of the minimum period of vitality; and when it occurs at other periods, we may readily believe that it is due to fortuitous circumstances, or occurs in a state of system which in an unusual degree evinces the characters of the human system in general at the minimum period of vitality. Cholera, in its various outbreaks in England, has followed a similar progression, and has proved itself to be essentially a disease of the minimum period of vitality.

The following table shows this fact in a striking manner, in the two outbreaks of 1832 and 1849, by the percentage of deaths which occurred in England in the months of May, June, July, August, September, October, and

November :

TABLE showing the MONTHLY PROPORTION per Cent. of all the DEATHS from CHOLERA in 1832 and 1849.

|

in its power in various parts of the world, and hence will vary in its capability to resist morbid agencies.

Enteritis and gastritis produce their maximum of mortality in the second and third, or decreasing and minimum, quarters, whilst there was a defect on the average in both diseases in the maximum period of vitality, and in gastritis the defect was continued even into the increasing period.

The greatest mortality from the plague in England occurred at the minimum period of vitality.

The various attacks of the disease known as the Plague, which occurred in London in the sixteenth and seventeenth centuries, exhibited the same features as the cholera of our day in reference to the question now under discussion, and show a remarkable similarity in the essential nature of the two diseases, as the following extracts from a table copied into the same report from Mr. Marshall's work on the Mortality of the Metropolis very clearly show :

TABLE showing the WEEKLY NUMBER of

DEATHS from the PLAGUE in LONDON in the various Epidemics, contrasted with the usual Mortality in other Years.

2.41

0.60

4:40

3.76

27

13:57

13.91

28

28.69

29.17

23

17.71

37:46

13.19

8.55

2.59

1.55

32

278

1503

2256

3583

3014

There was thus a progressive increase in the mortality from cholera through June and July to the maximum mortality in August in 1832, and through June, July, and August to the maximum in September 1849, and thenceforward in both years there was a rapid decline. These facts show a great preponderance of mortality in the two months when the vital actions were at the minimum.

It is interesting to notice that the month of maximum mortality from cholera was earlier in Paris than in this country-viz., in June in 1849, and even in April in 1832; but there is so great a want of uniformity in the progression of the monthly returns from that city that we are tempted to doubt if the records have been well kept, or if the features of this disease were the same in Paris as in London. It is, however, highly probable that a disease which is so closely connected with the degree of vital power of the body will exhibit different manifestations in different countries and climates, for the human constitution certainly differs

In each of these outbreaks it will be seen that the great development of the attack occurred in July, and reached its maximum point in the minimum months of vitalityviz., in August and September, whilst in November the disease had nearly disappeared.

The greatest mortality in chest diseases is found in the periods of increasing and maximum vital action, and the least mortality at those of minimum vital action.

This is shown by the deaths from bronchitis,

pneumonia, and pleuritis, and especially in bronchitis, in which the extreme difference was so great as a defect of nearly 11 per cent. in the minimum and an excess of nearly 13 per cent. in the maximum period. There is no exception to be found in the returns in these two directions; but in reference to the second quarter of the year, in which there is a mixture of influences, we find that whilst the deaths from bronchitis were then in defect, those from pneumonia and pleuritis were still in excess a fact doubtless owing to the admixture of the returns in April and May with those in June.

Pericarditis followed precisely the order of pneumonia, and had its maximum at the period of maximum vital action, and vice versa, and the defect in the summer season was so much as 6 per cent.

Brain diseases prevail in the cold season. Apoplexy and epilepsy exhibited an excess of deaths in the increasing and maximum periods of vitality, and convulsions were in excess at the latter period only, whilst in all these diseases there was the least mortality at the periods of decreasing and minimum action. Eruptive aiseases for the most part prevail at the seasons of change.

This is a part of the subject worthy of the most profound study, and one which is Lecessarily most complicated in its details, for at the same period we find the confluence of two sets of causes which are antagonistic to each other, and which have to be reconciled by the system exposed to their influence. In the end of the struggle the conditions of the advancing season gain the mastery, but in the earlier period we are subjected to the evils of the soft, sensitive, perspiring skin of the end of summer being exposed to the rude equinoctial blasts, the enfeebled powers of assimilation struggling more or less feebly to supply the increased vital transformation which the cooler weather demands, and the active pulsation of the heart opposed by the lessened action of the skin, which, being accompanied by contraction of the capillaries, offers an unusual obstacle to the current of the blood at the surface, and causes it to accumulate in the internal parts. These and other antagonistic influences are doubtless the cause of much autumnal disease, just as in the contrary conditions of spring we find spring diseases, all of which are due to the antagonistic influence of a new order of external phenomena upon a system which may not be able to adapt itself quickly enough to those novel influences.

We do not purpose to enter at length into this interesting question, but will only point

ments or diversities to be met with in these seasonal diseases.

Scarlatina and typhus show a remarkable correspondence under this head, since both were most fatal in the increasing periods of vitality, and the least so in the next quarter, when the vital powers were the highest. Measles and scarlatina offer as remarkable a contrast, for the greatest mortality from the former occurred at the period of decreasing and the latter at that of increasing vital changes. Smallpox offered less diversity than might perhaps have been expected (the cases of death are happily now few), but the least mortality was found with low vital action.

In seeking to connect epidemics and eruptive diseases with certain states of vitality of the system, we must especially bear in mind the caution already given, that the nature of the season will exert a great effect not only upon the type of that attack of the disease, but upon the month in which the maximum or minimum mortality will occur. Hence we are prepared to find that there was a retrocession in time in the epidemic of scarlatina in 1844 and 1848, and it is probable that measles will scarcely be more fatal in the second than in any other quarter if the spring and summer be cold. But these do not materially affect the general rule, that measles will be more fatal at the beginning of summer and scarlatina at the beginning of winter.

The type of a disease has also reference to the conditions of the system which preceded its occurrence.

This consideration is especially applicable to autumnal diseases, which occur with an increasing, but immediately follow the period of minimum, state of the vital powers. It has been often stated in the preceding pages that there is a progressive decline of the vital actions during two or three months at the middle and end of summer; but the minimum period is not an extended one- not so extended as the maximum period in the springand hence the upward tendency, which occurs at the middle of September, induces a somewhat sudden change in the vital actions, and during this period of change eruptive diseases, as scarlatina, are very apt to occur. It is therefore easy to understand that the type of a disease, commencing immediately on the occurrence of this change, will have more reference to the period of low vital power, which has just passed over, than that of the same disease appearing when the upward tendency has become well developed. The former would exhibit adynamic and the latter dynamic conditions.