264- 



RESPIRATION, ORGANS OF. 



fibres proceed, under a modified form how- 

 ever, over the walls of the intercellular pas- 

 sages and air-cells. The muscular and fibrous 

 structures are discoverable in the walls of the 

 bronchi 'after these latter have penetrated 

 within the bounds of the lobuli ; but never 

 the cartilaginous. This latter element, how- 

 ever, exists in the walls of the smallest of the 

 extra-lobular bronchi. 



The extreme end of each bronchus is the 

 common mouth of the infundibulum of Rossig- 

 nol ; the peduncle of the pulmonary vesicles 

 of Reisseissen ; the origin of the interlobular 

 passages of Addison. 



The bronchi divide on no constant or regular 

 plan. Small branches sometimes proceed 

 from a large stem, at different angles, from 

 every point of its circumference. 



Fig. 210. 



M 



!SS?< 



^zS^ 



^S 7 /^ 



yT 



CvT 



% 



^^c^^v^ ^^'/x^s^M 



^ /(^P^^jK^ 



^ w/r \ ,^>r^, } Ni 



Diagram of portions of the human lung imperfectly 

 injected with wax, exhibiting the mode in which 

 the intercellular passages a, a, a, spring from the 

 ultimate bronchi b, b. These are smooth-walled, 

 those alveolated. (Original.) 



Frequently they multiply dichotomously 

 (6, fig. 210.) 5 that is, a single tube divides 

 into two of equal diameters. Sometimes the 

 main bronchus exhibits a zigzag outline, the 

 branches proceeding from the alternate angles. 

 This latter method obtains with great con- 

 stancy in the case of the intralobular bronchi. 

 The number of branches within the lobule 

 into which a bronchus subdivides bears a 

 general proportion to the size of that lobule. 

 In the smallest, the intercellular passages 

 begin from two or three bronchial peduncles ; 

 in the largest, from eight or ten. In some 

 instances a second or supplementary bronchus 

 enters a lobule at the side. It is, however, 

 the rule, that each lobule is supplied only 

 with a single central bronchus. The point 

 of attachment of the bronchus is the apex () 

 of the lobule (6) ; the opposite point being 

 the base. The angle of division in the bron- 

 chial tree is, for the most part, the obtuse. 



This disposition of the tubes favours, mecha- 

 nically, both the ingressing and the egressing 

 column of air.* 



It has been maintained by Dr. Radcliffe 

 Hall I, that the contractility of the bronchial 

 tubes is called into action rhythmically in 

 each expiratory movement, to assist in emp- 

 tying the lungs. But no evidence has been 

 adduced in support of this doctrine. If the 

 contraction of the bronchial tube, through 

 muscular or any other force, occurred at the 

 first stage of the act of expiration, it is ob- 

 vious that it would arrest rather than favour 

 the egress of the air. It is not, however, im- 

 probable, that a certain regulated power over 

 the outgoing column of air is exerted by the 

 parietes of the bronchial tubes. This is more 

 likely to consist in a shortening and length- 

 ening of the tubes. They may also 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 supply of blood to the organs 

 to which they proceed. J It may possibly 

 be through this channel that the remark- 

 able variation is effected in the amount of 

 respiration which adapts the quantity of heat 

 produced to the depression of the external 

 temperature. It has been further suggested 

 by Dr. W. Gairdner $ that the contractility of 

 the smaller bronchi may serve to expel col- 

 lections of mucus which may accumulate 

 within them, and which neither ciliary action 

 nor the ordinary expiratory efforts suffice to 

 displace. 



Ultimate pulmonary tissue. Lobules. 

 Historical bibliography. From the dawn 

 of anatomy to the present age, " the struc- 

 ture of the lungs " has proved a fertile theme 

 for disputation. Anterior to the era of Mal- 

 pighi, anatomists were wont to regard the 

 Jungs as consisting of " a spumous tissue," in 

 which air and blood became directly inter- 

 mixed. Malpighi|| first demonstrated the 

 untenableness of this view. He placed the 

 fact beyond doubt, that the air and the blood 

 were contained in separate channels.f He 

 described the air-cells, and contended that 

 they communicated among themselves, but not 

 with the blood passages. 



In the year 1665, Bartholin wrote to de- 



* " Rien n'est plus varie' que la longueur de ces 

 rameaux, le mode de ramification qu'ils subissent, 

 le nombre de leurs subdivisions et la direction que 

 celles-ci affectent. On peut cependant les rapporter 

 a deux types principaux : le premier comprend les 

 tubes aeriens qui sont soumis au mode de division 

 par ramifications akernes ; le second, ceux qui sub- 

 issent la loi de dichotomic ou de trichotomie." Re- 

 cherches sur la Structure intime du Poumon de 

 1'Homme, &c. par M. Rossignol. Bruxelles, 1846. 



j- Trans, of Prov. Med. Assoc. 1850. 



J Carpenter, Principles of Human Physiology, 

 p. 514. 



Edinburgh Monthly Journal, May, 1851. 



|| Marcellus Malpighi, Opera omnia, Lugd. Ba- 

 tav. 1687, p. 320. Lettre premiere. 



<jf " Ex trachea in ipsas mox ex una in alteram 

 patens sitaditus et tandem desinent in contiuentem 

 membranum." 



