VI.

The influence and value of pure and healthy air may be seen in the simplest physiological observations.

Animal life is fed and sustained by respiration, as well as vegetable life. It is from the blood that animal life derives the materials and forces which maintain it, and we have seen how this owes its vivifying properties, in a great measure, to the oxygen which it receives from the respiratory organs, and how its power is in direct ratio to the purity of the air breathed. A vitiated atmosphere manifests itself at once in the nutritive powers of the vital stream; and the more feeble the respiration, the less rich the blood. This "oxygen enters by the lungs into the blood, and with the blood flows on and circulates through the body; it also enters partly into the composition of the tissues, so that it is a real food, and it is as necessary to the construction of the human body as the other forms of food which are usually introduced into the stomach."

The weight of oxygen, says Professor Johnston, taken up by the lungs, exceeds considerably that of all the dry, solid food which is introduced into the stomach of a healthy man.

Man consumes one hundred gallons of air every hour, ordinarily with eighteen respirations per minute, and two hundred and six cubic feet of air is the minimum for the preservation of health. The minimum allowed to the English hospitals by artificial ventilation is twenty-two hundred cubic feet the hour. The patients of St. Guy's receive four thousand cubic feet of fresh air every hour. The quantity required by the sick is enormous, to compensate the products of respiration, and all the deleterious evaporations of the locality where they are placed, and all other effluvia of diverse natures. In the Hospital Lariboissaire, at Paris, where about fifteen hundred cubic feet of air are furnished by machinery every hour, a taint is perceptible in the atmosphere: and Morin, in his experiments at Hospital Beaujon, thought that two thousand cubic feet were hardly sufficient. Dr. Sutherland believes four thousand feet to be necessary. The quantity, however, is nothing compared to quality. The quality is of the highest importance. The air must contain the vivifying properties of its normal constitution, or it loses force, and death must ensue. The source of animal heat is in the mutual chemical action of the oxygen and the constituents of the blood conveyed by the circulation. When the atmosphere is impure the oxidating processes are much diminished. We receive into our lungs about one hundred gallons of air per hour, and from this we absorb about five gallons of oxygen, or about one twentieth of the volume of air inspired.

"The essential and fundamental condition of all respiration is the reciprocal action of the nourishing fluid, and a medium containing oxygen." Dumas believes that oxygen is necessary to the conservation of the vitality and proper structure of the globules of the blood; also that the integrity of these organisms is one of the essential conditions to the arterialization of the nourishing stream.

Milne Edwards, also, maintains that the great absorbing powers of the blood exist in the globules. The normal number of these globules is one hundred and twenty-seven out of the thousand component parts of the blood; but they vary according to the barometer of health; sometimes they are observed in disease to descend to sixty-five. Vierodt has shown how a certain limit in the number of blood globules in the mammalia cannot be passed in the descending scale without death taking place. Simon and others have also shown how a careful and nutritious regimen may increase these globules in the blood of the consumptive, bringing them up from sixty-four to even one hundred and forty-four.

The blood of man is the richest of all the mammalia, and it contains, according to Berzelius, three times as many hydrochlorates as the blood of the ox.

Its richness depends upon the species and individual, and also upon the degree of health, it varying according to the condition of the person.

"A diseased pathological condition causes a diminution in the proportion of active principles of the nourishing fluid, and especially in fibrine, of which the abundance is allied to the most important activity of the vital work in some parts of the organism." "The blood," says Dr. Jones, "is not only distributed by innumerable channels through every recess of the body; the blood is not only the source of all the elements of structure; the blood not only furnishes the materials for all the secretions and excretions, and for all the chemical changes,--but the blood is in turn affected by the physical and chemical changes of every vessel, of every nerve, of every organ and texture of the body. It is evident then that the constitution of the blood will depend upon the food, upon the vigor and perfection of the organs of digestion, respiration, circulation, secretion, and excretion; upon the vigor and perfection of the nervous system, and of all the organs and apparatus; and upon the correlation of the physical, vital, and nervous forces. The character of the blood will then vary with the animal; with the organ and tissue through which it is circulating; with the age, sex, temperament, race, diet, previous habits, occupation, and previous diseases; with the soil and climate; and with the relative states of the activity of the forces."