PHYSICAL PROPERTIES OF THE LUNGS. 225 



trunks being usually found in a section of a large bronchial tube. These nerves 

 lie outside the cartilages, and are in close relation with the branches of the 

 bronchial arteries. Medullated and non-medullated nerve-fibres occur in the 

 nerves, which also contain numerous small ganglia (Remak, Klein, Stirling). In 

 the lung of the calf these ganglia are so large as to be macroscopic. The exact 

 mode of termination of the nerve-fibres within the lung has yet to be ascertained 

 in mammals, but some fibres pass to the bronchial muscle, others to the large 

 blood-vessels of the lung, and it is highly probable that the mucous glands are also 

 supplied with nerve filaments. In the comparatively simple lungs of the frog, 

 nerves with numerous nerve-cells in their course are found (Arnold, Stirling), and 

 in the very simple lung of the newt, there are also numerous nerve-cells disposed 

 along the course of the intra-pulmonary nerves. Some of these fibres terminate in 

 the uniform layer of non-striped muscle which forms part of the pulmonary wall 

 in the frog and newt, and others end in the muscular coat of the pulmonary 

 blood-vessels (Stirling). The functions of these ganglia are unknown, but they 

 may be compared to the nerve-plexuses existing in the walls of the digestive 

 tract.] 



The Function of the Non-striped Muscle of the entire bronchial 

 system seems to be to offer a sufficient amount of resistance to increased 

 pressure within the air-passages; as in forced expiration, speaking, 

 singing, blowing, etc. The vagus is the motor-nerve for these fibres, 

 and according to Longet (1842), the "lung-tonus" during increased 

 tension depends upon these muscles. Stimulation of the lower end of 

 the vagus causes a slight contraction of the bronchial muscles, but the 

 movement is neither sudden nor considerable. It is highly doubtful if 

 bronchial (spasmodic) asthma depends upon contraction of these mus- 

 cular fibres due to stimulation of the vagus. 



Chemistry .In addition to connective, elastic, and muscular tissue, the lungs 

 contain lecithin, inosit, uric acid (taurin and leucin in the ox), guanin, xanthin (?), 

 hypoxanthin (dog) soda, potash, magnesium, oxide of iron, much phosphoric 

 acid, also chlorine, sulphuric and silicic acids in diabetes sugar occurs in 

 purulent infiltration glycogen and sugar in renal degeneration urea, oxalic acid, 

 and ammonia salts ; and in diseases where decomposition takes place, leucin and 

 tyrosin. 



[Physical Properties of the Lungs. The lungs, in virtue of the large 

 amount of elastic tissue which they contain, are endowed with great elas- 

 ticity, so that when the chest is opened, they collapse. If a cannula with 

 a small lateral opening be tied into the trachea of a rabbit's or sheep's 

 lungs, the lungs may be inflated with a pair of bellows, or elastic pump. 

 After the artificial inflation, the lungs, owing to their elasticity, collapse 

 and expel the greater part of the air. As much air remains within 

 the light spongy tissue of the lungs, even after they are removed from 

 the body, a healthy lung floats in water. If the air-cells are filled 

 with pathological fluids or blood, as in certain diseased conditions of 

 the lung (pneumonia), then the lungs or parts thereof may sink in 

 water. The lungs of the fcetus, before respiration has taken place, 

 sink in water, but after respiration has been thoroughly established in 



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