INNERVATION OF BRONCHIAL MUSCLE FIBRES. 309 



Yawning consists of a deep inspiration accompanied by a wide 

 opening of the mouth and of the glottis, often attended by movements 

 of the arms. 



Cheyne-Stokes respiration. A special modification of the 

 respiratory rhythm, known under the above title, occurs in certain 

 pathological cases. In this form the activity of the respiratory centre 

 becomes periodic. Thus the respirations gradually decrease in ampli- 

 tude until they cease altogether. After a pause of greater or less duration, 

 a feeble inspiration ensues, to be succeeded by a somewhat stronger one, 

 and the inspirations gradually return to, or somewhat above, their 

 normal height, to then undergo a diminution as before. Mosso 1 has 

 shown that, even in the normal state, a certain periodicity during 

 respiration may be observed during sleep. Well-marked Cheyne- 

 Stokes breathing has often been observed in cases where there was 

 increased cerebral pressure or deficient blood supply to the brain. 

 Langendorff 2 discovered that a similar condition might be produced in 

 frogs by ligature of the aorta, or by cutting out the heart, or by poison- 

 ing with muscarin. In the latter case, the phenomenon could not be 

 abolished by subsequent administration of atropin. In animals a 

 periodic respiration has sometimes been observed when a section between 

 the brain and the medulla oblongata has been carried out too low, so as 

 to affect the respiratory centre injuriously. Although we can assume 

 with a high degree of probability that the cause of the Cheyne-Stokes 

 phenomenon is to be sought in a morbid condition of the respiratory 

 centre, we are not yet in a position to form a definite conclusion as to 

 the exact changes involved in this condition. 



THE INNERVATION AND ACTION OF THE BRONCHIAL 

 MUSCLE FIBRES. 3 



A contraction of the smooth muscle fibres which surround the large and 

 smaller air tubes must have several effects, namely (1) A constriction of the 

 bronchi or bronchioles. (2) A diminution of the air space of the lungs, and 

 therefore, in the absence of compensatory changes in blood contents, of the 

 volume of the whole lung. (3) An increased resistance to the passage of the 

 air into and out of the alveoli. 



From the time when Longet, 4 from direct observation of the bronchioles, 

 concluded that the vagus nerve carried motor fibres to the bronchial muscle, 

 the subject has been investigated by a number of physiologists. Although 

 in some cases purely negative results were obtained, the accuracy of Longet's 

 statement must be accepted as beyond doubt. Among those who obtained 

 evidence of bronchial constriction by various methods, more or less imperfect, 

 may be mentioned Schiff, 5 Paul Bert, 6 Gerlach, 7 MacGillavry, 8 Roy and Brown, 9 



1 Arch.f. Physiol., Leipzig, 1886, Suppl., S. 37. 



2 Ibid., 1880, S. 241 ; 1881, S. 33. 



3 This chapter is based on the very full accounts of the subject given by Einthoven, 

 "Ueber d. Wirkung d. Bronchialmuskeln, etc.," Arch.f. d. ges. Physiol, Bonn, 1892, 

 Bd. li. S. 367; and by Th. Beer, "Ueber d. Einfluss d. peripheren Vagusreizung auf d. 

 Lunge," A rch.f. Physiol., Leipzig, 1892, Suppl., S. 101. 



4 Compt. rend. Acad. d. sc., Paris, tome xv. p. 500. 



5 Arch.f. d. ges. Physiol., Bonn, Bd. iv. S. 226. 



6 " Le9ons sur la physiol. comp. de respiration," Paris, 1870, p. 375. 



7 Arch.f. d. ges. Physiol., Bonn, Bd. xiii. S. 491. 



8 Arch, neerl. d. sc. exactes, etc., 1877, S. 445. 



9 Journ. Physiol., Cambridge and London, 1885, vol. vi. 



