tages. So also with our farming settlements. I have sought information from medical correspondents, chiefly by propounding queries relating to the causes of malaria, and find that the considerations, which determined their site, were convenient access to water, rivers, or roads. Whether the soil and surroundings are fit for a healthful residence is a secondary question. High situations are apt to be avoided, because too windy, and low ground preferred because more accessible, and because springs are more common here, and wells more easily dug. Hence farm settlements are often placed in the immediate vicinity of wet meadow land, scarcely above the water-line; or else on the springy soil which is frequently found at the foot of a hill; or else on the "hardpan," which, at all levels, crops out here and there between strata of gravel, and which, by holding the surface water, is always wet and cold. It is not more difficult, therefore, to discover the causes of consumption in such surroundings than it is to explain the relative prevalence of the same disease in certain localities in the coast region already mentioned, where, owing to the damp and chilling oceanic winds during Summer, as well as Winter, the maximum mortality is found. Common sense, therefore, naturally suggests drainage of soil and sewerage, which is the other means above referred to as best calculated for arresting, not only malarial diseases, but also consumption. And it is a singular confirmation of the value and importance of this simple hygienic measure, resulting from observation and comparison exclusively, and without any preconceived ideas, that the English physicians, while entirely ignorant of the discoveries of Dr. Bowditch, arrived at the same conclusions. In eighteen hundred and sixty-five-sixty-six, inquiries were made in England, under Government authority, into the effect of certain sanitary works and regulations designed to promote the public health. In pursuance of this inquiry, twenty-four towns were selected in which improved drainage had been established. It appeared, that while the death-rate had greatly diminished, it was most strikingly evident in the smaller number of deaths from consumption. In commenting upon this fact, the chief medical officer reports, that "the novel and most important conclusion suggests itself, that the drying of soil, which has, in most cases, accompanied the laying of main sewers in the improved towns, has led to the diminution, more or less considerable, of phthisis.

As I have proceeded in writing this paper, the subject has so grown upon my hands that I have barely alluded to many important points, such as drainage of soil and sewerage, which will receive due attention in the next biennial report of the State Board of Health. Thanking you for your patient attention I must now close, merely expressing the hope that what I have said will be seriously considered.

[As no criticism adverse to the views advanced has been received since the reading of the above paper, it is fairly presumable that it is in general accordance with the opinions entertained by the medical gentlemen to whom it was presented for indorsement.]-Secretary State Board of Health.

ON FOREST CULTURE AS A PROPHYLACTIC TO MIASMATIC

DISEASES.

BY W. P. GIBBONS, M. D.

[Read before the Alameda Medical Association, May 3d, 1875.]

It has not been proved, though asserted until belief is established, that the aroma of the eucalyptus is effective in preventing the incubation of intermittents. The exceeding rapid growth of the tree is dependent on the quantity of water which is accessible to its roots. The proverbially unhealthy atmosphere of swamp land is due to stagnant water. Where currents are established by drainage or by excess of water, the cause of malarious fevers, if not entirely removed, is materially abated; it would be removed if the drainage were complete. Let us look at the results which naturally follow the planting and cultivation of some kinds of forest trees. In eight years the eucalyptus will attain a diameter of eighteen inches and a height of fifty feet. Experiments which I have made determine these facts: A branch of this tree which contains one hundred and five square inches of leaf-surface, will absorb 3.25 ounces of water in eighteen hours. The entire tree will furnish an area of three hundred and ten thousand five hundred square inches of leafsurface, and the amount of water daily absorbed by the roots would equal six hundred and nine pounds, or seventy-six gallons. Given a stagnant swamp of two hundred acres, each acre having two hundred trees, and the amount of water daily absorbed by the roots would be three million and forty thousand gallons, or four hundred and five thou sand three hundred and thirty-three cubic feet. This would be equal to a constant stream, running at the rate of three miles per hour, of two feet wide and six inches deep.

This question has a practical import, as applied to two projects which are now being discussed, and to the results on public health which would follow the adoption of either; the irrigation of the San Joaquin Valley, and the introduction of the water of Lake Tulare into San Francisco for economical purposes. The direct effect of irrigating the low lands of the valley would be the formation of a larger area within which malarial fever would prevail; for it is well known that there are lands along the San Joaquin, the Merced, and some of their tributaries, dry during the Summer months, but which, on being plowed, liberate the subtle poison which engenders disease. Farmers, without exception, have experienced this, in having every member of the family prostrated with intermittents. Physicians are cognizant of many places where the upturning of dry meadow soil, for agricultural purposes, has been followed by malarial fever. During the construction of the Central Pacific Railroad along the San Joaquin Valley, nearly every laborer became a victim of the same disease. The great district in California which is subject to malarial fevers includes large portions of the Sacramento, the San Joaquin, and the Tulare Valleys, extending from the

sixth standard north from Mount Diablo base to the eighth standard south, covering an area of three hundred and seventy-five miles in length, with a width varying from two to twenty-five miles. Much of this low land is known as tule swamp, from its being covered with Scirpus lacustris I., which grows in places from eight to twelve feet high. Other portions have a dense undergrowth of willow, which disappears in the neighborhood of the tules, but which reasserts its claim to the watery soil in places along the whole course of the valley. Outside the willows and the swamp, is a sandy alluvium, which comprises the arable portion of the soil.

This immense field of swamp and overflowed land, covering an area of over six thousand square miles, has comparatively little population outside of Sacramento, Stockton, Marysville, and other cities, which are feeders to the agricultural and mining population. Hence, it is difficult to estimate the area which may properly be regarded as malarial.

Will extensive irrigation change the climatal condition of a district of country? The question has been practically answered in the mining districts of California and elsewhere. Before the formation of ditches and the damming of the upper waters of rivers which form tributaries of the Sacramento and San Joaquin, the surface moisture of land among the mountain foothills was generally evaporated by the middle of May or the first of June. At this time clouds ceased to form in the upper air, and by day and night the unbroken clearness of the sky during the Summer solstice permitted the full intensity of solar heat to impinge on the denuded soil. The heat thus acquired during the day was seldom radiated with sufficient rapidity in the night to bring the temperature of the air within range of the dew point. In fact, during the latter part of Summer, the air was almost absolutely dry. The absence of dew thus became a marked feature of the interior climate.

After the headwaters of the rivers had been dammed, and ditches to the extent of seven thousand miles constructed, which spread water during most of the Summer through thousands of smaller channels, the air became so charged with vapor that deposits of dew became the rule instead of the exception. No other change was manifest except a slight reduction of temperature as a sequence of evaporation. Beyond the results thus foreshadowed in mining operations, and the certainty of securing fair crops, there is nothing to be urged in favor of extensive irrigation as compensatory to giving greater activity and diffusion to malarial poisons.

The matter of cultivating forests becomes then a question of almost vital importance to every settler within the precincts of this low land. It is not a doubtful experiment as a hygienic measure. The medical faculty need not be reminded of the conditions which increase the virulence of, or which destroy malarial poisons. Observation has established as facts: that excess of water in soil, by producing currents which carry off the poison or dilute it to the extent of rendering it obnoxious, prevents the formation of miasma; and that a lack of water in soil, by abstracting a necessary factor to vegetable decomposition, also prevents the development of disease. It is between these extremes that the forces operate which render active the toxic properties of marsh miasm. There must be added, however, a temperature ranging upward from sixty degrees Fahrenheit, and prolonged for weeks or months, before all the conditions which are necessary to produce vegetable decomposition and miasm are fairly established.

What then is the modus operandi by which forests purify the atmos

phere and prevent the formation of marsh miasm? It has been stated that six thousand square miles of the great valley are included in overflowed lands, and this amount may be reclaimed. (1) Let us so enlarge the experiment detailed on a previous page as to make a belt of eucalyptus trees two miles wide, and extend it three hundred and seventyfive miles, or the entire length of the valley. Nature works by small accretions, but operates on a large scale. She would of herself execute all the work which is here laid out, were she allowed a little time. But the aggressive spirit of Yankeeism must accomplish tremendous results within a few years of business life. It cannot tolerate the idea of using up a few centuries out of the storehouse of eternity, in order that a piece of swamp land or a section of arid debris should be converted into a spot befitting fifty bushels of wheat to the acre. Fortunately for science, this spirit was not "peeking" round in the paleozoic age, as all transitions between the awkward Silurian and the post-tertiary eras would have been totally ignored.

A forest of the before-named magnitude would contain ninety-six million trees, and during every twenty-four hours there would be exhaled seven billion two hundred and ninety-six million gallons, or nine hundred and eighty million cubic feet of water. This would be sufficient to fill a ditch fifty feet wide, nine and five tenths feet deep, and three hundred and seventy-five miles long, which, flowing from each extremity of the valley to its outlet in San Pablo Bay at the rate of three miles per hour. would require two days to empty itself. The water taken up and exhaled by such a mass of trees would be equivalent to a constant stream of this volume.

This estimate represents the capability of daily absorption. The quantity of water which would actually be thus taken from the soil may fall far short of this amount, for the ground, not being always saturated, would afford but a limited supply to the roots. The range in quantity between fact and theory will not affect the argument, inasmuch as there is always maintained, in living organizations, a definite, yet varying degree of activity between the functions of the system and its consumption of food.

But absorption of water, and its subsequent exhalation, do not constitute the process of nutrition and growth in the vegetable world. The water of the soil not merely holds in solution all the solid mineral matter which goes to make up the substance of the tree, but gaseous elements, either in a simple form, as of atmospheric air; or combined, as in carbonic acid, sulphureted hydrogen, and other mephitic gases. Whatever there may be held in solution is, in a general sense, absorbed by the roots and conveyed, with little or no change, to the leaves, which form the laboratory of the vegetable world. Carbon, hydrogen, lime, potassa, soda, and other substances, are here subjected to changes, by the agency of solar light and heat, which adapt them to the composi tion and the structure of the tree. This chemical activity is rapid in many growths, especially in the eucalyptus. The strong aroma of its gum is diffused to a distance of thirty or forty feet. The hydrogen, which forms one of its elementary constituents, is derived from the decomposition of water which the tree takes from the soil. The entire

(1) Land Office Report, 1868.

process of vegetable life constantly carried on in effecting the assimilation of food, not only returns to the atmosphere oxygen, as a product of the decomposition of water and carbonic acid, but restores the purity of all other substances that are exhaled either in a simple or compound form. Thus, in whatever shape marsh miasm may exist-whether held in solution by water and diffused in the vapor of night, or retained in the soil and liberated by the presence of water-it is certain to be destroyed by an adequate development of forest growth. This is so fully recognized in medical literature as to render exemplifications unneces sary.

As another sequence of the activity of vegetable growth, the cooling of the atmosphere is prominent. This reduction of temperature is mainly due to exhalation of water from the leaves. This function is most active during the day; for the more rapid the evaporation the cooler does the air become; consequently, the greatest difference of temperature between the open air and the shade of a tree is from noon until three o'clock P. M. This range, being affected by local causes, cannot be precisely and uniformly indicated, except by actual experiment. Where the thermometer stands in the shade at 85° Fahrenheit, it will be at 100° in the sunlit air, protected from direct solar rays; at the same time the surface soil will indicate 115°. This is the breathing temperature prevalent for parts of several months along the great valley of which we have spoken. At times 130° or 140° is indicated by the thermometer. It is very common for the night temperature to stand at 80° or upward. At such times the incubation of disease is

active.

Unless the conditions be peculiar, a maximum temperature of 80° through the day will be followed by a minimum temperature below 60° during the night. Along seashore counties the thermal range is not so great, and in valleys protected from ocean breezes the radiant heat during night arrests the cooling process from inflowing air.

Let us see what disposition would be made of the vast amount of liquid daily absorbed and discharged into the atmosphere. At 212° a cubic foot of water will be converted into one thousand six hundred and ninety-six cubic feet of vapor. At 60°, with the barometer at thirty inches, each cubic foot of air will contain 6.22 grains of vapor. The nine hundred and eighty million cubic feet of water will saturate a belt of atmosphere three hundred and seventy-five miles long, ten miles wide, and one thousand two hundred feet in thickness, which would be resting over the valley for the greater portion of every twenty-four hours. But would the swamp land yield this quantity of water every day? Estimating the average rainfall at eighteen inches, and excluding the inflowing water from mountain streams, it would require over eight hundred days for the forest to absorb all the moisture that the valley received during the Winter months. If this process commenced with the active growth of vegetation in February, and were to continue but one hundred and twenty days, all the requirements of growing crops would be met, without appropriating over one sixth of the amount which fell upon the land. Moreover, there would be a compensating action constantly going on, in consequence of the vapor, rendered to the atmosphere, being partially returned to the soil by condensation.

The arid nature of parts of the San Joaquin Valley is not referable to high temperature and evaporation alone. In the middle of the plains, east of Stockton, excavation shows a succession of strata formed of washed bowlders and coarse gravel, more than seventy feet in depth,