CHAP, ii.] 



RESPIRATION. 



LSI 



stimulation of a nerve-fibre at a part of its course by means of 

 an electric current is at best a rough process, by which we can- 

 not hope to do more than approximate to the results actually 

 taking place in the living body when the nerve is stimulated at 

 its endings by natural stimuli ; and the approximation is { r- 

 haps less in the case of the exquisitely sensitive respiratory 

 centre than in many other cases. 



If in an animal in which a careful graphic record of tin- 

 respiratory movements is being taken, the trachea be suddenly 

 closed at the summit of an inspiration, the result is a pause 

 before the succeeding inspiration follows, that is to say, a 

 partial or temporary inhibition of inspiration ; and if during 

 such an experiment on a rabbit a curve be taken by means of 

 the isolated slip of the diaphragm, 259, it will be seen (Fig. 

 96 A) that the slip elongates somewhat ; that is to say, previ- 

 ously in a state of slight tonic contraction, it changes in tin- 

 direction of expiration. If on the other hand the trachea l>- 

 suddenly closed at the end of an expiration (Fig. 96 B), when 



B 

 FIG. 96. EFFECTS OF DISTENSION AND COLLATOR or LOTTO. (Head.) 



Both curves are described by a lever attached, as stated in $ 869, to a slip of 

 the diaphragm of a rabbit. A contraction of the diaphragm (inspiration) rate* 

 the lever ; during relaxation of the diaphragm, the lever falls. 



In A, the trachea is closed at x, the height of inspiration ; a pause f 

 during which the lever gradually sinks until an inspiration (a very powerful one) 

 sets in. 



In B, the trachea is closed at the end of expiration, z ; there follow power 

 inspirations. 



31 



