PKACTICAL CONDUCT OF EXERCISE XI 147 



The insertion of the cannula into the artery close distal to a side branch tends to avoid 

 interruption by clotting. 



Obs. 51. If the Ringer-Locke be too cool, e. g. 20°-25° C, the flow through the kidney 

 is very slow, perhaps only 4 drops per 20", instead of some 15 drops per 20" as is usual 

 with the Ringer-Locke at 36° C. 



EXERCISE XII 



To provide for this and other student exercises a decerebrate preparation the following 

 is a serviceable method, a feature in it being the employment of the ' decerebrator '} 



i. The animal, deeply anaesthetized, is placed supine on the operating table, with all 

 four limbs retracted symmetrically by a clip-weight attached to each foot. 



ii. A short string is passed by means of a small packing-needle horizontally through 

 upper lip, entering below one nostril and emerging below the other ; this is tied in a reef- 

 knot not quite close to the lip, and in it is caught a hook the string of which carries a 100- 

 grm. weight hanging over the end of the operating table. This keeps the neck and head 

 steady and extended. 



iii. Through a short median incision in the cricoid region the common carotids r. and 1. 

 are tied or looped close below their thyroid branch. 



[iv. A tracheal cannula may be inserted, preferably low down, e. g. 2 cm. above sternum, 

 because less irritative to the respiratory centre than if higher. In tying in the cannula thus 

 low down care is taken not to include the recurrent laryngeal nerves running up beside the 

 trachea. The insertion of a tracheal cannula is for most exercises merely a precaution lest 

 breathing should lapse for a time after decerebration, and artificial ventilation be then needed.] 



V. The animal is then placed prone, the clip-weights are detached from the fore-paws 

 and the fore-limbs flexed at elbow and shoulder supporting the chest ; a warm bottle 

 is placed under the pelvis, relieving the abdomen from pressure against the table. A median 

 incision is made along the scalp back to occiput exposing in front the fronto-parietal suture 

 of the skull. In old animals, where there may be difiiculty in detecting the suture, it can be 

 revealed by slightly smearing the cranium with blood, or by pressing on the cranial vault 

 with the handle of the scalpel so as to cause a yielding at the suture which a blood smear then 

 makes evident. From the suture, without regard to the little forward or backward running 

 dentation which its median 3-4 mm. often shows, 30 mm. are measured off backward along 

 the median line, and the point so reached is marked by a small cross-cut slightly notching 

 the median ridge. For a large animal 31-32 mm. should be allowed instead of 30 mm. 

 The point lies about 6 mm. in front of external occipital eminence. 



vi. The animal, still deeply anaesthetized, is next placed on the 'decerebrator,' set ready 

 on a table, preferably a low one. 



The decerebrator consists of a wooden frame (text-fig. 46) supporting an inclined block 

 (n, text-fig. 46) on the front face of which slides a yoke-piece (y, text-fig. 46) fixable at the 

 desired height by a clamp. The head of the deeply anaesthetized animal is given a suitable 

 inclination by pushing the open mouth over the upper end of the phlanged piece (t, text-fig. 

 46) of a steel plate fixed to the front face of the inclined block. The flange running upward 

 from the steel plate lies above the tongue in the mouth. The upper edge of the steel plate 



1 Sherrington, Jnl. of Physiol, vol. xlix, 1915, Proc. Physiol. Soc. p. Hi : Miller and Sherrington, 

 Quart. Jnl. of Physiol, vol. ix, p. 147, 1916. 



U 2 



