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in the venous blood (22 mm. Hg), and of the difference of the carbonic acid tension in the venous blood (41 mm. Hg), and in the air cells (27 mm. Hg), it might be concluded that the passage of the gases might be due solely to pressure. The absorption of oxygen, however, does not follow absolutely the law of pressures; that chemical processes are involved is shown by the union of oxygen with the hemoglobin of the blood corpuscles. The exhalation of Co, is also partly a chemical process, as it has been shown that the quantity excreted is greatly increased when oxygen is simul. taneously absorbed. Oxygen not only favors the exhalation of loosely combined CO2, but favors the expulsion of that which can only be excreted by the addition of acids to the blood.

Changes in the Blood during Respiration.

As the blood passes through the lungs it is changed in color, from the dark purple hue of venous blood to the bright red scarlet of arterial blood.

The heterogeneous composition of venous blood is exchanged for the uniform composition of the arterial.

It gains oxygen and loses carbonic acid.
Its coagulability is increased. Temperature is diminished.

Asphyxia.—If the supply of oxygen to the lungs be diminished and the carbonic acid retained in the blood, the normal respiratory movements cease, the condition of asphyxia ensues, which soon terminates in death.

The phenomena of asphyxia are, violent spasmodic action of the respiratory muscles, attended by convulsions of the muscles of the extremities, engorgement of the venous system, lividity of the skin, abolition of sensibility and reflex action, and death.

The cause of death is a paralysis of the heart, from over distention by blood. The passage of the blood through the capillaries is prevented by contraction of the smaller arteries, from irritation of the vasomotor center. The heart is enfeebled by a want of oxygen and inhibited in its action by the inhibitory centers.

ANIMAL HEAT. The Functional Activity of all the organs and tissues of the body is attended by the evolution of heat, which is independent, for the most part, of external conditions. Heat is a necessary condition for the due performance of all vital actions; though the body constantly loses heat by radiation and evaporation, it possesses the capability of renewing it and main.

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taining it at a fixed standard. The normal temperature of the body in the adult, as shown by means of a delicate thermometer placed in the axilla, ranges from 97.25° Fahr. to 99.5° Fahr., though the mean normal temperature is estimated by Wunderlich at 98,6° Fahr.

The temperature varies in different portions of the body, according to the degree in which oxidation takes place; being the highest in the muscles during exercise, in the brain, blood, liver, etc.

The Conditions which Produce Variations in the normal temperature of the body are : age, period of the day, exercise, food and drink, climate, season, and disease.

Age.At birth the temperature of the infant is about 1° F. above that of the adult, but in a few hours falls to 95.5° F., to be followed in the course of 24 hours by a rise to the normal or a degree beyond. During childhood the temperature approaches that of the adult; in aged persons the temperature remains about the same, though they are not as capable of resisting the depressing effects of external cold as adults. A diurnal variati of the temperature occurs from 1.8° F. to 3.6° F. (Jürgensen); the maximum occurring late in the afternoon, from 4 to 9 P. M., the minimum, early in the morning, from 1 to 7 A, M.

Exercise.—The temperature is raised from 1° to 2° F. during active contractions of the muscular masses, and is probably due to the increased activity of chemical changes; a rise beyond this point being prevented by its diffusion to the surface, consequent on a more rapid circulation, radiation, more rapid breathing, etc.

Food and Drink.—The ingestion of a hearty meal increases the temperature but slightly; an absence of food, as in starvation, produces a marked decrease. Alcoholic drinks, in large amounts, in persons unaccustomed to their use, cause a depression of the temperature, amounting from 1° to 2° F. Tea causes a slight elevation.

External Temperature.- Long-continued exposure to cold, especially if the body is at rest, diminishes the temperature from 1° to 2° F., while exposure to a great heat slightly increases it.

Disease frequently causes a marked variation in the normal temperature of the body, rising as high as 107° F. in typhoid fever, and 105° F. in pneumonia; in cholera it falls as low as 80° F. Death usually occurs when the heat remains high and persistent, from 106° to 110° F.; the increase of heat in disease is due to excessive production rather than to diminished elimination.

The Source of Heat is to be sought for in the chemical decompositions

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