Cellular respiration

“ Inasmuch as the gaseous interchange between the lungs and the blood takes place only in the terminal air sacs it follows that, at the end of each respiration, the rest of the respiratory tract is filled with air low in oxygen and high in carbon dioxide, which on inspiration is drawn back into the lungs, diluting the fresh air. ”

“ Nearly one-third of the excretions of the body are eliminated through the lungs. The average adult contaminates about five thousand cubic inches of air with every breath. The importance of having an abundant supply of pure air at all times is obvious.
In ordinary respiration an adult abstracts sixteen cubic feet of oxygen from the atmosphere every twenty-four hours, and adds to it fourteen cubic feet of carbonic acid in the same time. ”

“ We must, however, distinguish between respiration by the lungs, called external respiration, and respiration by the cells, called internal respiration.
The purpose of respiration is indicated by the changes that take place in the air while it is in the lungs. Air entering the lungs in ordinary breathing parts with about five per cent of itself in the form of oxygen and receives about four and one half per cent of carbon dioxide, considerable water-vapor, and a small amount of other impurities. ”

“ A definite increase in the volume of the lungs is the consequence of frequent repetition of this supplemental respiration. The air-cells which are as a rule inactive, and which are reserved for cases of excessive respiratory strain, arise from their inaction; their walls, which are usually collapsed, and even stuck together, separate and give entrance to the air which can not find room in the confined space sufficient for ordinary breathing. ”

“ The excretion of carbonic acid and absorption of oxygen are mainly performed by the lungs, in creatures which have lungs; but in such creatures there continues a certain amount of cutaneous respiration, and in soft-skinned batrachians like the frog, this cutaneous respiration is important. ”

“ The quality of the air for breathing has also been much improved by the admixture of a considerable proportion of oxygen with the air supplied, so that one respiration of this oxygenated air is only required where many respirations of non-oxygenated air would be needed. ”

“ Besides ordinary respiration in which free oxygen is taken up, there is, in plants as in animals, a so-called intramolecular respiration, in which fixed oxygen in highly oxidized compounds serves to carry on respiration. The newer investigation has acquainted us in no equivocal way with the power of motion—yes, even with the sensibility of plants. ”

“ It may be further noted that natural respiration is accompanied with, first, the distension of the air cells of the lungs with air; and, second, with an increased flow of blood into the organs, beyond that necessary for their nourishment and growth. They thus increase in absolute weight, while their specific gravity is lessened. ”

“ Their respiration is the effect of a sort of affinity between their substance and the vital gas—a chimiotactism directing them toward oxygen. This may be illustrated by forming a microscopic preparation of fresh lymph, imprisoning a few bubbles of air, and sealing it hermetically with paraffin. After two or three hours we can see the leucocytes grouped around the bubbles. When the provision of air is exhausted, several hours afterward, the leucocytes will cease to move and become inert. On inserting a needle, the contact of the air revives them. ”

“ In this case after a time the pulmonary capillaries, like the cutaneous ones, act with increased energy; the breathing, which was before quick, and the air thrown out at each respiration in less quantity, and cool to the back of the hand opposed to it, now becomes larger in quantity, and warmer than natural; which however is not accompanied with the sensation of heat in the membrane, which lines the air-vessels of the lungs, as in the skin. ”

“ Much more, when we discern a mighty power, that of expansion, and see how the Almighty has made our frame in reference to its production by caloric—the lungs allowing of heat within them like wet cloth, and the nerves, bones and muscles all made and arranged, so that oxygen shall be brought to them by respiration on the one hand, and carbon by the numerous digestive and circulatory organs on the other. ”

“ The respiratory, or breathing process, is not instituted for the benefit of man alone, for we find it both in the lower order of animals and in plant life. Nature is very economical in the arrangement of her plans, since the carbonic acid, which is useless to man, is indispensable to the existence of plants, and the oxygen, rejected by them, is appropriated to his use. In the lower order of animals, the respiratory act is similar to that of the higher types, though not so complex; for there are no organs of respiration, as the lungs and gills are called. ”

“ The functions of the heart, the brain and the lungs are intimately associated. Oxygen is indispensable for the life of the tissues, and its supply is dependent upon the integrity of the three organs mentioned, which have been called the tripos of life. Respiration is brought about by the stimulation of certain nerve cells in the brain, the most effective stimulus to these cells being a diminution of oxygen in the blood supplying them. These cells send out impulses to the muscles concerned in inspiration, the chest expands, and air is taken into the lungs. ”

“ First, the obliteration of numerous capillaries in the pulmonary system, occasioned by the thinning and destruction of the cell-wells in which they ramify, interferes with oxygenation, so that an increased number of inspiratory acts is required to supply the deficiency, and thus respiration is hurried; and, secondly, the impairment of the natural elasticity of the air-vesicles prevents the expulsion of their contents ”

“ From what has been said, it will be understood that oxygen may be employed in respiration, at any rate for a limited time, when the respiratory organs suffer under certain forms of suffocation and impediment to breathing. ”

“ Then, gradually, physiologists began to perceive that pulmonary or external respiration had to do primarily with the exchange of gaseous materials and that oxidation did not occur in the lungs, neither to any degree in the circulating blood, but rather in the different tissues and organs of the body where activity of various sorts prevails. ”

“ And hence the absorbents of the lungs are less able to fulfil the whole of their duty. And part of the thin mucus, which is secreted into the air-cells, remains there unabsorbed, and occasions the difficult respiration, which awakes the patient. And the violent exertions of the muscles of respiration, which succeed, are excited by the pain of suffocation, for the purpose of pushing forwards the blood through the compressed capillaries, and to promote the absorption of the effused lymph. ”

“ Circulation and Respiration.—Does water have free access to the body cavity? Does the hydra have few or nearly all of its cells exposed to the water in which it lives? From its structure, decide whether it can breathe like a sponge or whether special respiratory cells are necessary to supply it with oxygen and give off carbon dioxide. Blood vessels are unnecessary for transferring oxygen and food from cell to cell. ”

“ But if the air which the patient breathes be too highly charged with vapour, it is easy to understand how the sensibility of the nerves of the heart may be paralysed, notwithstanding their power to bear somewhat more of this agent than the brain and nerves of respiration. I calculated (p. 74) the quantity of chloroform which would suffice to arrest respiration in the adult of average size to be thirty-six minims, provided it were equally diffused through the circulation; but supposing a patient breathes, at any time, air containing ten per cent. ”

“ The specific gravity was 0·605 in one instance, and 0·798 in the other. As many of the animals died in a way resembling asphyxia, the respiration ceasing before the circulation, it might at first be supposed that we should meet with the same congestion of the lungs; but by the time that the respiration is altogether suspended by the action of chloroform, that agent has begun already to influence the heart, which does not inject the blood into the lungs with the same force as when the respiration is mechanically prevented, whilst it is in full vigour. ”

“ Part 21 The explanation of the admission of air and respiration in those animals in which a lung is found, and especially in those in which it is full of blood, is to be found in the fact that it is of a spongy nature and full of tubes, and that it is the most fully charged with blood of all the visceral organs. All animals with a full-blooded lung require rapid refrigeration because there is little scope for deviation from the normal amount of their vital fire; the air also must penetrate all through it on account of the large quantity of blood and heat it contains. ”

“ It follows also, from the principles which are above established, that respiration is a mixed function, a function placed as it were between the two lives, to which it serves as a point of contact, belonging to the animal life by its mechanical functions, and to the organic life, by its chemical functions; and hence we have the reason no doubt, why the existence of the lungs is as much connected with that of the brain, as with that of the heart. ”

“ A new element of many thousand pounds weight then presses upon the surface of its body. This atmospherick fluid, adulterated in cities with innumerable impurities and feculencies is drawn into its lungs: its diaphragm and muscles of respiration then begin to act, the lungs expand, and the respiration commences. The passage between the auricles of its heart and arterial duct are gradually closed up; the sphere of the circulation is extended; the whole current of blood in its frequent revolution hourly, passes through the lungs ”

“ Animals that breathe air through lungs have little air cells, so very small that a human lung is said to contain 600 millions of them; and these lie in contact with the capillary circulation of the lung which receives the oxygen and gives out the carbon. Some air-breathers have no lungs, but merely spiracles or minute holes in the body through which the air enters, coming in contact with the circulation. ”

“ In connexion with this subject it may be stated that, after a single ordinary inspiration of hydrogen gas, 6-ro respiration's of ordinary air must occur before the expired air ceases to contain some trace of hydrogen.
Types of Respiration.—The visible characters of respiration in man vary considerably according to age and sex. In men, while there is a moderate degree of upheaval of the chest, there is a considerable although not preponderating degree of excursion of the abdominal walls. ”

“ There are some observations on chemical physiology, and especially with regard to respiration, in the book on antimony which show their author to have anticipated the true explanation of the {67} theory of respiration. He states that animals breathe, because the air is needed to support their life, and that all the animals exhibit the phenomenon of respiration. He even insists that the fishes, though living in water, breathe air, and he adduces in support of this idea the fact that whenever a river is entirely frozen the fishes die. ”