BY DR. BURDON-SANDERSON. 805 



minims of a ten per cent, solution of chloral into the crural 

 vein. For this purpose the abdominal cavity must be opened 

 in the linea alba, immediately below the cnsiform cartilage, and 

 then two incisions must be made, extending from the opening 

 in opposite directions parallel to the edges of the costal car- 

 tilages, according to the instructions given in 56. Another 

 method consists in merely making an opening in the linea alba, 

 close to the cnsiform cartilage, sufficient to receive the finger, 

 the tip of which must be pressed against the centrum tendi- 

 neum, when the movements can be appreciated with great ex- 

 actitude. The plan most used consists in introducing a long 

 and slender needle into the chest through the eusiform carti- 

 lage, close to the lower end of the sternum, the direction of 

 which is such, that it grazes the upper surface of the diaphragm, 

 if possible piercing it at one or two points, so as to be in some 

 part of its course on the abdominal side of the membrane. 

 For this experiment, the rabbit must be carefully chloralized, 

 and secured on Czermak's supporter in such a way that the 

 spinal column is immovable. A long silk thread is then passed 

 through the eye of the needle and connected with the little 

 bow-wood pulley shown in fig. 250, the movements of which 

 are inscribed by means of the horizontal lever on the blackened 

 cylinder. The tracing so obtained enables us not only to de- 

 termine to what relative distance the dome of the diaphragm 

 descends in each inspiratory act, but also the mean relaxation 

 of the muscle, z.*e., the mean height to which it ascends during 

 each expiration. This, as we shall see further on, is much 

 affected by conditions which act on ihe muscle by its motor 

 nerve. 



92. Intercostal Muscle*. To demonstrate the action of the 

 intercostal muscles, a rabbit is used which has been deprived 

 both of voluntary motion and of sensibility b}- the ablation of 

 the cerebral hemispheres as well as of the corpora striata and 

 thai ami optici. This operation is performed as follows : The 

 animal having been rendered insensible by chloroform, both 

 carotids are tied. It is then secured on the supporter in the 

 prone position. The calvarium is now exposed by an incision 

 extending from the occiput to the frontal region in the middle 

 line, and the integument drawn aside in either direction. The 

 parietal bones having been first perforated with the trephine, 

 to allow of the introduction of the cutting pliers, the roof of 

 the cranium is rapidly removed so as to expose the hemi- 

 spheres completely. These organs are then scooped out with 

 the ivory handle of a scalpel, an assistant being at hand with 

 the actual cautery to arrest the bleeding. The animal at once 

 passes into a state resembling deep sleep, breathing regularly, 

 but much more slowly than before the operation. The action 

 of the respiratory muscles of the chest can now be investigated 

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