1.5 inches Weak 2.0 inches.
2.0 " Ordinary 2.5 " 4.5 " Remarkable 5.8 " 7.0 " Very extraordinary 10.0 " The co-operation of the resilience of the lungs and the elasticity of the walls of the chest with the expirtotory muscular movement, is probably the cause why the expiratory power, as tested by the height of a column of mercury, is greater than the inspiratory power. Dr. Hutchinson calculates that a man who raises 3 in. of mercury by an effort of inspiration exerts a force equal to 1000 lbs.; while the one remarkable case in which the mercury rose to 7 in., indicated it force of 2200 lbs., or nearly one ton.
The following points in connection with the respiratory movements require notice. Every complete net of respiration is divisible into four parts—viz.: 1. Inspiration; 2. A short pause, not always observed; 3. Expiration; and 4. A considerable pause, occu pying. according to Vierordt, about one-fiftL of the whole time required for one com plete respiratory act. The act of expiration is always more prolonged than that of inspi ration, the former to the latter in the ratio of 12 : 10 in adult males, and as 14 : 10 in children, women, and aged persons. The number of respiratory acts performed in a minute varies at different ages. According to Quetelet, at birth there are 44 respirations in one minute; at 5 years of age, 26; from 15 to 20, 20; from 20 to 25, 18.7: from 25 to 30, 16; from 30 to 50, 18.1: so that from 16 to 20 may be taken as the ordinary range for healthy adults, although Hutchinson gives the wide range of from 6 to 40. average ratio which the number of respirations bears to the number of pulsations in a given time is about 1 : 4i, and if there is any great deviation from this ratio, there is probably some . . .
ob=truction to the of the blood, or some disorder of the nervous system. Thus, in pneumonia tor inflammation of the lungs), in which a greater or less amount of pul monary tissue Is unfitted for its office, the number of the respirations increases in a more rapid proportion than the number of pulsations, so that the ratio becomes as 1 : 3, or even as 1 : 2. In hysteria, a similar or even greater deviation front the normal ratio may occur; and Elliotson records a case in which the respiratory movements were 9S, or even 106, while the pulse was 104. On the other hand. in certain typhoid conditions, and in narcotic poisoning, the respiratory nets are diminished in number; the ratio of respiration to pulsations being as 1 : 6, or even 1 : 8.
We have next to inquire into the mode in which the muscular movements of respira tion are kept tip by nervous power. "There can be an doubt," says Dr. Carpenter, " that these movements, though partly under the control of the will, are essentially automatic' in their nature. Their chief centers consist of two ganglia; corresponding to the origins of the pneumogastric nerves, which are the principal excitor nerves which convey the stimulus on which these movements are dependent; whilst from the adjacent parts of the medulla oblongata and spinalis proceed the chief motor nerves by which they are carried into effect. And thus it happens that the whole of the encephalon may
be removed from above, and the spinal cord (as far up as the origin of the phrenic nerve) from below, without suspending the most essential of the respiratory movements." —Principles of Raman Physiology (6th ed., 1864, p. 274).- It would early us far beyond our assigned limits to notice the interesting series of phenomena that follow the division or irritation of the various branches of the pueumogastric nerve. We may, however, mention that when the trunks of this nerve are divided on both sides, the respiratory movements still go on, although with diminished activity. Hence, there must he other excitors to the action of the respiratory muscles. Amongst these the nerves distributed to the general surface, and particularly to the face, probably perform an important part; and in exciting the first inspiration, the fifth pair seem the principal agent. In support of this view, Dr. Carpenter adduces the well-known fact, that the first inspiratory effort of the new-born infant is must vigorously performed when the cool external air collies in contact with its face. Dr. Marshall Hall, in his New Memoir on the True Spinal Mar row, p. 29, relates a case in which the first inspiration was delayed simply because the face was protected from the atmosphere by the bedclothes; the instant they were lifted up, the infant breathed. Many familiar facts demonstrate the influence of the super ficial nerves on the respiratory system in the adult as well as in the infant. "Every one," to use Dr. Carpenter's words, "knows that the first plunge into cold water, or the first descent of the stream of the shower-bath, or even the dashing of a glass of cold water in the face, will produce inspiratory efforts; and this fact has many important practical applications. Thus, in the treatment of asphyxia, whether congenital or the result of narcotic poisoning, drowning, etc., the alternate application of cold and heat is found to be one of the most efficacious means of restoring the respiratory movements, and a paroxysm of hysterical laughter may be cut short by dashing a glass of cold water in the face." The principal motor or efferent nerves concerned in bringing out the respiratory movements are the phreni c, going to the diaphragm ; the intercostal, supplying the intercostal muscles; the facial and the spinal accessory nerves; although, as has been already mentioned, the superficial nerves generally exert a motor or efferent action.