GENERAL STRUCTURE OF THE RESPIRATORY ORGANS. 367 



Pneumogastrics. 1 It is remarked by Dr. Williams, that the contractility of 

 the bronchial muscles is soon exhausted by direct stimulation ; but that it 

 may in some degree be restored by rest, even when the lung is removed from 

 the body. When the stimulation is long continued, however, as by intense 

 irritation of the mucous membrane during life, the contractile tissue passes 

 into a state which resembles the tonic contraction of muscular fibre. The 

 contractility is greatly affected by the mode of death, and is remarkably 

 diminished by the action of vegetable narcotics, particularly stramonium 

 and belladonna ; whilst it seems to be scarcely at all affected by hydrocyanic 

 acid. These facts are very important, as throwing light upon certain dis- 

 eased conditions. It has long been suspected, that the dyspnoea of Spasmodic 

 Asthma depends upon a constricted state of the smaller bronchial tubes, 

 excited through the nervous system, frequently by a stimulating cause at 

 some distance ; and there can be now little doubt that such is the case. The 

 peculiar influence of stramonium and belladonna, in diminishing the con- 

 tractility of these fibres, harmonizes remarkably with the well-known fact 

 of the relief frequently afforded by them in this distressing malady. It 

 seems not improbable that the contractility of the bronchial tubes may serve 

 to regulate the supply of air to the lobules, in accordance with the wants of 

 the system, just as the contractility of the minute arteries regulates the sup- 

 ply of blood to the organs to which they proceed ; and it may possibly be 

 through this channel, that the remarkable variation is effected in the amount 

 of respiration, which adapts the quantity of heat produced to the depression 

 of the external temperature ( 282). It has been further suggested by Dr. 

 W. T. Gairdner, 2 that the contractility of the smaller bronchi may serve to 

 expel collections of mucus which have accumulated in them, and which 

 neither ciliary action nor the ordinary expiratory efforts suffice to displace. 

 286. The elasticity of the lungs, which in many animals, as the horse, is 

 remarkably increased by the dense layer of elastic tissue by which they are 

 invested, 3 plays an important part in the respiratory acts. Donders * esti- 

 mates the expiratory force derived from the elasticity and muscular tension 

 of the lungs, and coming into play in ordinary respiration, as equal to a 

 pressure of about 5 oz. on the square inch ; but the elastic tension is rapidly 

 increased by the dilatation of the lungs with air, and the carefully conducted 

 experiments cf Dr. Hutchinsou 5 led him to estimate it at certainly not less 

 than i? Ib. upon each square inch of surface, when the lungs have been filled 

 by the deepest possible inspiration ; so that its whole amount (reckoning an 

 average surface of 300 sq. in. for the male, and 247 sq. in. for the female) 

 will be not less than 150 Ibs. for the male, and 123 Ibs. for the female. 

 This force is exerted in aid of the e.cpiratory movement, and is directly 

 antagonistic to the inspiratory ; so that the inspiratory muscles must over- 

 come it, in order to produce complete distension of the pulmonary cavities. 



1 Volkmann (Wagner's Handworterbueh, Bd. ii, Art. Nervenphysiologie, p. 586), 

 Longet (Anat. et Physiol. du Systeme Nerveux, torn, ii, p. 289), and P. Bert (Legons 

 sur la Physiologic comparee do la Respiration, Paris, 1870, p. 375) affirm that it can, 

 whilst Kosenthal (Die Atliembewegunijen, p. 232), Rugenberg (Sludinn des Phys. 

 Institut zu Breslau, 18(i3, p. 47), and Wintrich (Krankheit. d. Resp. Org. in V'ir- 

 chow's Handbuch der Pathol., 1855-57) maintain that if a manometer be inserted 

 into the trachea, irritation of the peripheric extremity of the Vagus never produces 

 any increase of pressure, which would certainly occur if the capacity of the bronchi 

 diminished. 



2 Edinburgh Monthly Journal, May, 18-il. 



3 See G. Gulliver's Note to Willis's translation of Wagner's Physiology, 1844, 

 p. 360. 



4 See his Essays in Henle and Pfeuffer's Zeitsch., Bd. iii and iv. 

 6 Cyclop, of Anatomy, Art. Thorax, vol. v, p. 1058. 



