"Minimum height for ratings herein mentioned, 5 feet and 4 inches, stripped; the candidate should be well developed, considering his age and height.

"Persons possessing a mechanical trade may be enlisted even if over twenty-five, provided they are under thirtyfive years of age.

"No person, except an honorably discharged ex-apprentice, shall be enlisted as a seaman unless he shall have been four years at sea, nor as an ordinary seaman unless he shall have been two years at sea before the mast. In both cases applicants shall be required to pass a satisfactory examination."

The general appearance of the applicant is also taken into consideration, and those that are uncleanly in their person or attire are discarded because they prove incapable of efficient training.

Recently the character of the teeth in applicants for both the naval and military service has been taken into consideration. It is evident that a man whose grinding and biting capacity is seriously impaired will more readily suffer from gastro-intestinal trouble than one with a full set of perfect teeth. The loss of five teeth, absent or unsound in any degree, is usually considered as cause for rejection; even the loss of three or four molars or incisors in the same jaw is sufficient to render a young man unfit for service in the navy.

Principal Diseases among Mariners.-The average strength of the active list of the U. S. Navy for the year 1899 was 20,019. The total number of admissions for disease was 12,794, and for injuries 2955, giving a ratio per 1000 of strength of 636.11 and 146.92, respectively. During the year there were admitted to the sick list, of the total force

Of the 943 cases of malarial diseases, nearly one-third were from the navy-yard and marine headquarters, Washington, D. C.; of the 134 cases of typhoid fever reported during the year, 49 were under treatment in the naval hospital, Newport, R. I. Of this number, 45 originated among the personnel of the training station, I was received from the torpedo station, and 3 from ships of the North Atlantic squadron.

ure.

CHAPTER XV.

SOIL.

THE nature of the soil in its relation to health is an important subject. The relation of the soil of a locality to the public health is dependent upon its intimate structSoils are composed of varying proportions of mineral, vegetable, and animal constituents. These constituents vary in size not only in different localities, but even in the same locality. The interstices of the soil are filled either with air or with water. A soil is moist or dry according to the preponderance of small- or large-sized soil-particles. The finer and more uniform the soilparticles, the greater the amount of moisture usually contained in the soil.

All soils are porous, and contain varying amounts of air and moisture. The relation of the soil to health is influenced by the amount and nature of the contained air and water. The degree of purity of the ground-air and ground-water is influenced by the amount and nature of the vegetable and animal organic matter contained in the soil, and the temperature of the locality-whether favorable or unfavorable to the decomposition of organic matter through the agency of bacteria.

Ground-air.-Ground-air is usually rich in carbon. dioxid, derived from decomposing organic matter in the soil. It is also very moist, because there is usually plenty of opportunity to take up moisture. It also contains decomposition-products, such as marsh-gas, hydrogen sulphid, and ammonia. This air is, consequently, not suitable for respiratory purposes. The amount of soil-air that gains access to houses under ordinary conditions is, however, so small that its influence prob

ably is not felt. In newly made soils, in which there is considerable decaying organic matter, there is some danger of the entrance of large amounts of ground-air into houses built on such soils unless special provision is made to exclude it. In such houses there should be cemented foundation walls and cellars, and the supply of fresh air should be derived from the outside at some distance above the ground. Unless the foundation walls and cellars are cemented, the houses, when warmed, may serve as immense chimneys in extracting the air from the surrounding soil.

Ground-water.-Ground-water is rain-water that has fallen upon the soil of the locality and penetrated its surface. It differs from stored rain-water according to the nature of the soil constituents. It is richer in dissolved solids, and contains also the products of decomposition derived from decaying organic matter in the soil. It contains also numerous bacteria derived from the soil. The relation of ground-water to health is directly dependent upon the presence or absence of pathogenic bacteria in the soil, and the presence or absence of mineral constituents derived from the soil which may be injurious to health, such as salts of calcium, magnesium, or iron in large amounts.

Pettenkofer's theory of the relation of soil moisture to typhoid fever and cholera is no longer tenable. We know now that the height of the level of the groundwater has no direct influence in the production of either of these two diseases. There is evidently an indirect relation between low ground-water and the development of these diseases, because at such times the drainage area of all wells is increased, and the polluting material in or upon the soil of a correspondingly greater area is conducted into the well. In the same manner, when drinking-water is derived from streams, there is greater opportunity for the entrance of concentrated polluting matter into the stream, and it exists there in a more concentrated form than in times of flood.

The relation of a damp soil to the greater prevalence of consumption, as originally pointed out by Bowditch, cannot be regarded as a direct one. The damp soil probably predisposes to colds and diseases of the lungs, and thus paves the way for the contraction of consumption. There is thus far no evidence that the bacillus of tuberculosis is capable of multiplying in damp soils.

The relation of damp, marshy soils to malaria has received a great deal of elucidation in recent years. It is believed at the present time that the malarial organism is contracted most frequently, if not entirely, through the sting of a particular genus of mosquito-Anopheles. These mosquitoes are usually indigenous to the soil of certain marshy localities, but thus far no definite relation between the nature of the soil of these localities and the prevalence of mosquitoes has been demonstrated. Marshy localities, when drained so as to prevent the development of mosquitoes, also become healthful and free from malaria. Where drainage is impossible, it is known that the application of some oil, such as crude petroleum, on the surface of the water will prevent the development of the mosquitoes and thus eradicate malaria from those localities.1

Damp soils are likely to be productive of diarrheal diseases, though these affections are most probably brought about by certain bacteria in the soil along with the detrimental influence of the dampness itself. The amount of decaying organic matter in and upon the soil is most probably in direct relation to the prevalence of diarrheal diseases in a locality.

In the same manner the amount of moisture in the soil will influence the prevalence of other diseases, such as rheumatism, bronchitis, pneumonia, and the exanthemata. The relation of soil moisture to these diseases is probably only an indirect one, in that it tends to lower

1 Recent studies in Africa indicate that probably other diseases, especially filariasis, are conveyed by species of mosquitoes.