248 



THE POPULAR SCIENCE MONTHLY. 



average healthy temperature is not abso- 

 lutely identical in every individual, but may 

 vary from 97.75 to 99. It is slightly 

 higher in infancy and old age than in ado- 

 lescents 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 com- 

 mon in febrile diseases. As a rule, the 

 daily minimum is about daybreak, or be- 

 tween 2 and 8 a. m. After this a rise be- 

 gins, and continues until late in the after- 

 noon, 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. Second- 

 ly, 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 differ- 

 ence of 20 Fahr. or more between the tem- 

 perature 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 exam- 

 ple, under the tongue, and even this eleva- 

 tion 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 eleva- 

 tion of temperature resulting from food 

 rarely amounts to 1 Fahr. Fourthly, the 

 temperature of the human body is influ- 

 enced 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 bod- 

 ily 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 la< 

 ter. Murchison. 



IMPURITIES OF WATERS. 



There are certain abnormal conditions 

 of waters, arising from natural or artificial 

 causes, that are not very clearly under- 

 stood, and which present interesting fea- 

 tures for study and investigation. The 

 water of Jamaica Pond, near Boston, af- 

 fords a somewhat remarkable illustration 

 of such changed condition, or sickness from 

 natural causes, at the present time. 



This pond, which is situated at a com- 

 paratively high elevation, has one small 

 feeding-stream, and an equally small out- 

 let ; it receives no artificial drainage, and 

 is not in a thickly-settled locality. Its wa- 

 ter 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 pe- 

 culiar condition which it presents again this 

 winter, also after two seasons of severe 

 drought. 



The water is not perfectly clear, ani 

 does not become so by standing ; it is 

 cloudy, but not colored ; its color and taste 

 are decidedly offensive, resembling water con- 

 taining putrefying animal matter ; these con- 

 ditions 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 condi- 

 tion of this water and its present peculiar 

 state to be as follows : one United States 

 gallon of each contains 



Nokmat.. Abnormal. 



Organic matter 1.S6 grains. 2.33 grains. 



Mineral matter 2.41 " 2.56 " 



Total weight of impurities 3.77 " 4.S9 " 



By filtration, through paper, the water be- 

 comes 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 



