quence of diminished nutrition and more ready evaporation, and the coloring-matter of the blood again becomes visible.

The tropical climate acts upon the elasticity of the tissues most probably in such a manner that the elasticity of the different tissue-fibers is increased through the action of the heat. This is shown not only in natives, but also in the descendants of Europeans born in the tropics, and manifests itself in greater joint movement. and in general sluggishness and relaxation.

Influence of Tropical Climate on Nutrition.— K. E. Ranke' made a study of the influence of climate on nutrition during a journey to South America.

The optimum temperature of the European with medium clothing is 15° to 18° C., if none of the other climatic factors produces any definite action. In a climate with a temperature of 18° to 22° C. there is increased evaporation of water, but no definite influence upon the appetite. In a climate of about 25° C., when the other climatic factors neither increase nor decrease the action of the temperature, there is a marked diminution in the appetite. With further increase in the temperature there is also further decrease in appetite, and at last it sinks below the requirements of an adult at complete rest. The protein nutrition does not sink below the maintenance minimum of the lower laboring-classes; each further diminution being made at the expense of the fats and carbohydrates. If there is opposition to this instinctive diminution of the appetite, pathologic effects manifest themselves: disturbance of the general comfort, increased temperature, and decrease of the natural resistance against infectious diseases. If the nutrition is constantly diminished below that required because of the heat elimination in a very hot climate, the deficient nutrition leads to dangerous consequences.

2

F. Hueppe states that the dangers encountered by Europeans in the tropics in regions of less than 2000 August Hirschwald, Berlin, 1900. 2 Berlin. klin. Wochenschr., 1901, p. 7.

meters' elevation are constant high temperature combined with high atmospheric humidity. These factors call forth increased efforts to cool the body, and hence affect the activity of the skin, heart, and lungs. The results of this increased activity are noticed in fatigue on slight exertion and decreased nervous and muscular power.

The high sensibility of the digestive organs of the European in the tropics is caused by the dilution of the digestive fluids from increased ingestion of fluids induced by the free perspiration. All these conditions vary in different individuals. General exercise, especially in the form of riding and swimming, is beneficial for all the body functions. The tropical climate operates especially unfavorably upon the female organism.

The greatest enemy of the European in the tropics is alcohol, the misuse of which increases enormously all the other unfavorable and detrimental influences. The infectious diseases, as yellow fever, cholera, plague, dysentery, and malaria, are the next greatest detrimental influences in the tropics.

The influence of climate upon the course of certain diseases has been the subject of numerous observations. The influence of a dry climate upon the course of tuberculosis is now well understood. The rarefied air as found in the Rocky Mountain region seems to be of great value in the treatment of this disease. This condition of the atmosphere produces an augmented respiratory activity which is highly beneficial in early stages of consump

tion.

The value of pine forests in localities having a dry, sandy soil and a climate of low relative humidity is also generally recognized. The pine belts of New York, New Jersey, and North Carolina are especially adapted for consumptives during the winter months of the year.

Probably the chief value of removal to another climate in the early stages of consumption is to be traced to the changed conditions of life. The outdoor life which these localities usually permit, along with the high percentage

of clear days, and the removal from the anxieties and constraints of business life, are as beneficial as the climate itself, if not more so. The conviction that this is the case has led a number of prominent physicians to advocate the high plateaus of the Blue Mountains in eastern Pennsylvania as a desirable locality for the recuperation of those likely to be benefited by change of climate. The locations which have been specially advocated are Pocono Mountain in Monroe County and Green Mountain in Lehigh County. This region is the natural home of the pine, though the operations of the lumbermen have long since caused its almost total disappearance. The State of Pennsylvania is acquiring a number of large areas of land in different parts of the State for forest reservations, and in time these will be valuable localities for the establishment of institutions for the climatic treatment of diseases similar to those found in the Adirondack region of New York and elsewhere.

Influence of Climate and Season on Mortality.The seasonal variations alone in the temperate zone are of great influence upon mortality aside from the general climatic conditions of a locality. Mild winters and cool summers both lower the mortality, the former exerting a special influence upon the aged, and the latter upon the young, more particularly the infantile population. A cool, damp summer is always accompanied by a low mortality. Season has also an important influence upon the character of the prevalent diseases-intestinal diseases. being most prevalent in summer and respiratory diseases in winter. Typhoid fever is least prevalent in late spring and early summer, and most prevalent in the autumn. Typhoid fever reaches its mean about the end of the year; then there occurs a gradual fall to a minimum in April, sometimes interrupted by a slight outbreak in January or February. There is also a June or July minimum with a more rapid rise to maximum about the end of October or beginning of November. The curve of scarlet fever is very similar to that of typhoid fever, but

its minimum is in March, and it rises gradually to a maximum early in November.

Acclimatization is that process by which animals or plants become adapted to, and so thrive in, a climate different from that in which they are indigenous. For instance, almost all the domestic animals were originally natives of warm climates. As regards man, Arnould

states that the race is acclimatized when it preserves (1) the natural increase in population; (2) its normal longevity; (3) its aptitude for physical and intellectual work. He gives the following as conditions favorable to the acclimatizing process: 1. Slight alteration in the latitude: to proceed from a warmer to a colder climate is an advantage. 2. Ethnical disposition. 3. Manners and customs. It is essential to adapt one's diet to the climate. Clothing and general habits should also be assimilated to the altered conditions of climate. 4. Aptitude for crossbreeding. 5. Soil and locality: where the soil is not unhealthy, acclimatization is much simplified; if an unhealthy soil is made healthy, by drainage, etc.

It is evident that a large part of the influences attributed to changes in climate is in reality due to the prevalence of certain diseases in different localities which are absent in others. For instance, those passing from the temperate zone into the tropical zone encounter diseases which are unknown in the temperate region, and for which they possess neither a congenital nor acquired immunity and hence are highly susceptible to such infections. After they have acquired an immunity against such diseases, it is probable that the more important feature of their acclimatization has been accomplished.

Ground-air. The atmosphere does not stop at the surface of the soil, but penetrates into all the pores and crevices. The proportion of air in the soil is not great where there are no fissures or clefts, but in the superficial layer air is always present in appreciable proportions, and especially so in made soil. Soil-air is of somewhat different composition than the atmospheric air. We find present in it large quantities of the products of putrefac

tion, which is very active in the soil. It is, therefore, far richer in carbon dioxid, besides containing other hydrocarbons as the result of putrefaction, principal among which is marsh gas. In subterranean caverns the air may have undergone such an amount of change as the result of putrefaction and chemical changes going on in the rocks that it is not fit for respiration, and may be highly inflammable as the result of the admixture of other gases. Soil-air is therefore injurious if inhaled in large quantities and for a long time. It tends to pene

trate into houses from the surrounding soil, because the warmer air of the house has an upward tendency and thus abstracts the air from the soil. For this reason newly made soil is considered unhealthy and should be avoided. This is especially the case with the newly made soil in and around cities, where the materials employed in making the soil are frequently such as are capable of undergoing putrefaction.

Sewer-air.-Sewer-air in properly constructed modern sewers is merely atmospheric air which contains a slight excess of carbon dioxid and small amounts of gases resulting from putrefaction taking place in the sewage. Consequently there is also a slight decrease in the proportion of oxygen present. The proportion of microorganisms is usually less than that of the air of streets and houses, and they are usually harmless species. The movement of air in sewers is rather slow, and affords abundant opportunity for the suspended particles, along with the micro-organisms, to become deposited on the moist walls of the sewer. When a portion of a sewer or the drainage-pipes of a house become obstructed, so that there is no longer a free circulation of air in the obstructed portion, then there is an accumulation of the gases resulting from putrefaction, such as carbon dioxid, hydrogen sulphid, marsh gas, etc., and these gases are highly injurious when inhaled in considerable quantities or in smaller amounts for a considerable time.

The Impurities in Air.-These are either gaseous or solid. The more important gaseous impurities in air are