384 OF RESPIRATION. 



the air-tubes, even when the lungs were found loaded with blood, and when 

 the respiration before death was very labored. This naturally leads us to 

 doubt whether the frothy serum is the cause of the labored respiration, and 

 of the congested state of the pulmonary vessels, in those cases where it is 

 present; though there can be no doubt that, when once it is effused, it must 

 powerfully tend to increase the difficulty of respiration, and still further to 

 impede the circulation through the lungs. Dr. Reid has satisfied himself of 

 an important point which has been overlooked by others, namely, that this 

 frothy fluid is not mucus, though occasionally mixed with it, but that it is 

 the frothy serum so frequently found in cases where the circulation through 

 the lungs has been impeded before death. From this and other facts, 

 Dr. Reid concludes "that the congestion of the bloodvessels is the first de- 

 parture from the healthy state of the lung, and that the effusion of frothy 

 serum is a subsequent effect." The experiments of v. Boddiirt 1 are essentially 

 confirmatory of those of Dr. Reid. He has shown, however, that effects, 

 similar to those following division of both Vagi, result from paralysis of the 

 inferior laryngeal nerve, which permits the entrance of foreign bodies into 

 the air-passages. It has also been demonstrated 2 that tracheotomy performed 

 after division of the Vagi prolongs life, the degree of prolongation depending 

 on the efficiency of the means used to prevent the entrance of foreign bodies 

 into the air-passages. If to these facts it is added that the injection of mucus 

 into the trachea and bronchi of animals with intact Vagi produces serious 

 effects, the inference, as Dr. Sanderson observes, is unavoidable that the in- 

 flammatory symptoms observed after section of the Vagi, are due to the 

 abolition of the guard which the glottis constitutes at the entrance to the 

 respiratory passages, and the entry of foreign bodies into their interior. 3 

 "The experimental history of the Par Vagum," it is justly remarked by 

 Dr. Reid, " furnishes an excellent illustration of the numerous difficulties 

 with which the physiologist has to contend, from the impossibility of in- 

 sulating any individual organ from its mutual actions and reactions, when 

 he wishes to examine the order and dependence of its phenomena." In such 

 investigations, no useful inference can be drawn from one or two experiments 

 only; in order to avoid all sources of fallacy, a large number must be made; 

 the points in which all agree, must be separated from others in which there 

 is a variation of results ; and it must be then inquired, to what the latter 

 is due. 4 



2. Effects of Respiration on the Air. 



306. The total amount of air which can be drawn into the Lungs by the 

 deepest possible inspiratory movement, by no means affords a measure of the 

 quantity which they ordinarily contain. It is in fact composed, as was first 

 pointed out by Mr. Julius Jeffreys, of several different quantities, which may 

 be distinguished as follows: 



1 Journal cle la Physiologic, vol. v, 1862, pp. 442 and 5L'7. 



- Sanderson, Handbook for the Physiological Laboratory, 1873, p. 308. 



3 Schiff (Archiv f. Phys. Heilkunde, Bd. vi) .suggests that the congestion results 

 from \a>o-niotor paralysis. 



4 On the important subject of the Mechanism of Respiration, the following Memoirs 

 may In- consulted in addition to those already referred to: Dr. J. Reid's Art. Res- 

 piration in Cyclop, of Anat. and Physio) , vol. iv ; Dr. Hutuhinson in Med.-Cliir. 

 Trans., vol. xxix ; Dr. Sibson in Phil Trans., 184", Med. Gaz., vol. xli, Mcd.-Chir. 

 Trans, vol. xxxi, and Trans, of Prov. Med. Assoc., 1850; Beau and Maissiat in 

 Archiv. Gen., 1842; Mendelssohn, Der Mechanismus der Respiration und Circula- 

 tion, Berlin, 1845; and Vierordt, Art. Respiration in Wagner's IIand\v6'rterlMich der 

 Physiologic, Bd. ii. 



5 Statics of tho Human Chest, 1843. 



