508 NUTRITION. 



temperature of the blood and saturated with the vapor of water, all loss of heat then 

 being impossible." In a number of experiments performed upon this principle, Prof. 

 Lombard failed to observe a sufficiently marked elevation of temperature to justify the 

 conclusion that the blood is cooled in passing through the lungs. These experiments can- 

 not be so positive as those made by introducing thermometers into the heart in living ani- 

 mals without opening the chest or disturbing the circulation; but they are important, in 

 connection with such observations, as failing to prove that the blood is either cooled or 

 heated in the lungs. From these facts it appears that there is no positive evidence of 

 any change in the temperature of the blood in passing through the lungs in the human 

 subject. In animals there probably exist no constant differences in temperature in the 

 two sides of the heart. When the loss of heat by the general surface is active, as in ani- 

 mals with a slight covering of hair, the blood is generally cooler in the right cavities ; 

 but, in animals with a thick covering, that probably lose a great deal of heat by the pulmo- 

 nary surface, the blood is cooler upon the left side. Undoubtedly there are refrigerating 

 influences in the lungs, both from the low temperature of the inspired air and from evap- 

 oration ; but these are equalized and sometimes overcome by processes in the blood itself. 



Variations at Different Periods of Life. The most important variations in the tem- 

 perature of the body at different periods of life are observed in infants just after birth. 

 Aside from one or two observations, which are admitted to be exceptional, the body of 

 the infant and of young mammalia, removed from the mother, presents a diminution in 

 temperature of from one to four degrees. In infancy the ability to resist cold is less than 

 in later years ; but after a few days the temperature of the child nearly reaches the stand- 

 ard in the adult, and the variations produced by external conditions are not so great. 



The experiments of W. F. Edwards have an important bearing upon our ideas of nu- 

 trition during the first periods of extra-uterine life. He found that, in certain animals, 

 particularly dogs and cats, that are born with the eyes closed and in which the foramen 

 ovale remains open for a few days, the temperature rapidly diminished when they were 

 removed from the bod.y of the mother, and that they then become reduced to a condition 

 approximating that of cold-blooded animals; but, after about fifteen days, this change in 

 temperature could not be effected. In dogs just born, the temperature fell after three or 

 four hours' separation from the mother to a point but a few degrees above that of the 

 surrounding atmosphere. The views advanced by Edwards are well illustrated in in- 

 stances of premature birth, when the animal heat is much more variable than in infants 

 at term, and in cases of persistence of the foramen ovale. 



In adult life there does not appear to be any marked and constant variation in the 

 normal temperature; but, in old age, while the actual temperature of the body is not 

 notably reduced, the power of resisting refrigerating influences is diminished very con- 

 siderably. There are no positive observations showing any constant differences in the 

 temperature of the body in the sexes; and it may be assumed that, in the female, the 

 animal heat is modified by the same influences and in the same way as in the male. 



Diurnal and other Variations in the Heat of the Body. Although the limits of varia- 

 tion in the animal temperature are not very extended, certain fluctuations are observed, 

 depending upon repose or activity, digestion, sleep, etc., .which it is necessary to take 

 into account. These conditions, which are of a perfectly normal character, may induce 

 changes in the temperature amounting to from one to three degrees. It has been ascer- 

 tained that there are two well-marked periods in the day when the heat is at its maxi- 

 mum. These, according to the most recent observations in Germany, are at eleven A. M. 

 and four p. M. ; and it is a curious fact, that, while all observations agree upon this point, 

 the very elaborate experiments of Lichtenfels and Frohlich show that these periods are 

 well marked, even when no food is taken. Barensprung and Ladame farther show that 

 the fall in temperature during the night takes place sleeping or waking ; and that when 



