NERVOUS MECHANISM OF RESPIRATION. 283 



In one method an elastic bag is inserted through an opening in the 

 abdominal wall, between liver and diaphragm. The elastic bag is connected 

 by a tube with a recording tambour. Each descent of the diaphragm in 

 inspiration presses on the bag, and the increased pressure transmitted to the 

 recording tambour can be recorded as a respiratory movement. 



Kronecker's phrenoyraph 1 consists of a lever, one broad spoon-shaped end 

 of which is inserted between the liver and diaphragm, while the other end is 

 connected by threads running on pulleys to a writing lever. Rosenthal's 

 phrenograph differs from the preceding in that the movement is transmitted 

 by air to a tambour instead of by means of threads. 



5. All these methods, however, surfer from the defect that, although they 

 directly or indirectly give a fairly correct record of the movements of the 

 respiratory apparatus, they are unable to discriminate between passive and 

 active movements. Thus, if the lungs be artificially distended, there will be a 

 descent of the diaphragm and 

 a movement of the phreno- 

 graph lever, just as if the 

 inspiration were brought 

 about by an active contrac- 

 tion of the muscle. In deal- 

 ing with the innervation of 

 respiration, we shall see that 

 it is very important to be able 

 to study the effect of artificial 

 inflation or collapse of the 

 lungs on the activity of the 

 respiratory muscles; and such 

 information can be only very FlG> IBS. Normal tracing of diaphragm-slips of 

 imperfectly afforded by any rabbit. (Head's method.) 



of the graphic methods al- 

 ready described. The method which best meets these difficulties is that 

 devised by Head. 2 This observer has shown that in the rabbit the 

 anterior part of the diaphragm, which is connected to the ensiform cartilage, 

 is so disposed that it may be isolated as two parallel slips from the rest of 

 the muscle without injury to the blood- or nerve-supply. These slips may be 

 clamped at the tendinous end, and the contractions recorded by a lever 

 attached by a thread to the other end, which is cut free from the cartilage. 

 It is then found that the slips contract synchronously with the rest of the 

 diaphragm, and their contractions (Fig. 168) may be taken as a sample of 

 the contraction of the whole diaphragm, while they are but little affected 

 by any passive movements which may be imparted to the thoracic wall. 

 The results arrived at by this method will be described later on. 



THE NERVOUS MECHANISM OF RESPIRATION. 



We have seen that each act of inspiration involves the contraction 

 of a number of muscles, which are added to whenever the need for 

 greater respiratory interchanges occurs. Expiration also, although 

 normally effected by the passive retraction of the stretched lungs and 

 costal wall, yet, with the smallest additional call on the respiratory 

 apparatus, involves the co-ordinated actions of a number of other 

 muscles. These co-ordinated rhythmical contractions must be initiated 

 in the central nervous system, and we have in this section to discuss 



1 v. Marckwald, "The Movements of Respiration," translated by Haig, London, 1888, 

 p. 9. 



2 Journ. PhysioL, Cambridge and London, 1889, vol. x. pp. 1 and 279. 





