average healthy temperature is not absolutely identical in every individual, but may vary from 97.75° to 99°. It is slightly higher in infancy and old age than in adolescents and adults. In the same individual also there are certain slight variations in the temperature consistent with health, some of which deserve to be mentioned. In the first place, there are diurnal variations of temperature constantly occurring in healthy persons, which must be kept in mind in reference to the diurnal variations so common in febrile diseases. As a rule, the daily minimum is about daybreak, or between 2 and 8 a. m. After this a rise begins, and continues until late in the afternoon, or to between 4 and 9 p. m. These daily fluctuations are somewhat greater in children than in adults; but in any case they rarely exceed 1° Fahr., and any variation in excess of this is very transient. Secondly, it is well known that muscular exercise increases the heat of the body, while repose tends to its reduction. The differences, however, resulting from this cause, are chiefly observed in the extremities. The temperature, in health, of the hands and feet, is often much below that of the trunk and internal parts. There may be a difference of 20° Fahr. or more between the temperature of the feet and that under the tongue. The effect of exercise is to raise the temperature of the extremities to that of the trunk. It produces little change—not more than an elevation of 1° Fahr. in the temperature of internal parts, as, for example, under the tongue, and even this elevation ceases on the cessation of exertion. Thirdly, the ingestion of food causes a slight rise of temperature. The effect of a full meal is to hasten the normal diurnal rise, or to postpone its fall; but the elevation of temperature resulting from food rarely amounts to 1° Fahr. Fourthly, the temperature of the human body is influenced to the extent of 1° or 2° by that of the surrounding atmosphere. Brown-Sequard found a rise of atmospheric temperature from 46.4° to 85.1° Fahr., to raise the bodily temperature from 97.9° to 100.22° Fahr. When the temperature of the atmosphere exceeds that of the normal standard of the human body, the temperature of the body occasionally exceeds the range compatible with health. It is also to be noted that young children and persons of advanced age have less power than adults of resisting external cold—the temperature of the body being more easily and considerably reduced by it in the former case than in the latter.—Murchison.
IMPURITIES OF WATERS.
There are certain abnormal conditions of waters, arising from natural or artificial causes, that are not very clearly understood, and which present interesting features for study and investigation. The water of Jamaica Pond, near Boston, affords a somewhat remarkable illustration of such changed condition, or sickness from natural causes, at the present time.
This pond, which is situated at a comparatively high elevation, has one small feeding-stream, and an equally small outlet; it receives no artificial drainage, and is not in a thickly-settled locality. Its water is still supplied, through pipes, to many citizens, and also to the neighboring towns of Brookline and West Roxbury. During the winter of 1866, after two seasons of drought, this water first exhibited the peculiar condition which it presents again this winter, also after two seasons of severe drought.
The water is not perfectly clear, and does not become so by standing; it is cloudy, but not colored; its color and taste are decidedly offensive, resembling water containing putrefying animal matter; these conditions are more evident when the water is heated, and are retained after evaporation to a small volume. Ordinary analysis shows the difference between the common condition of this water and its present peculiar state to be as follows: one United States gallon of each contains—
| Normal | Abnormal | |
| Organic matter | 1.36 grains. | 2.33 grains. |
| Mineral matter | 2.41 " | 2.56 " |
| Total weight of impurities | 3.77 " | 4.89 " |
By filtration, through paper, the water becomes clear and brilliant, the odor and taste of the filtered water being natural; and it is possible, in this way, to separate the offensive matter from the water and retain it for examination. This substance, which gives odor, taste, and additional weight to
