APPENDIX. 313 



posite the insertion of the carotid cannula is passed an iron rod, and by 

 means of clamps the ends of the rod are fixed to two stout retort stands. 

 A short piece of normal blood pressure tracing is taken on the drum 

 and then at a given moment the dog is placed in a vertical feet-down 

 position, by rotating the board (the dog must be carefully tied on the 

 board). The blood pressure falls, but shows some tendency to return 

 to normal while the dog is still upright. If the animal be very deeply 

 under an anesthetic there will be a very marked fall in blood pressure 

 with no tendency of the blood pressure to return, since the vasomotor 

 nerves and center are no longer able to compensate for the hydrostatic 

 effect of the blood in the vertical position (see p. 193). 



E. The Effect of Asphyxia on the Blood Pressure (see p. 195). 



A respiratory tambour is applied over the thorax or abdomen and 

 connected by tubing with a recording tambour, the writing point of 

 which is accurately adjusted so as to write in the same vertical line 

 as the writing point of the mercury manometer. The tubing coming 

 from the cannula is clamped and the effect of the resulting asphyxia 

 on the respiratory movements and on the arterial pressure is noted. 

 The three stages, as described on p. 000, should be obtained, but when 

 the third stage is reached the clamp must be removed from the trachea 

 so as to allow the animal to recover. 



Note 1, the slowing of the heart; 2, the gradual, often insignificant, 

 rise in blood pressure; 3, the effect of the respiratory movements on 

 the blood pressure. Both vagus nerves are cut and the above experi- 

 ment repeated, noting the difference in results. The rise in blood 

 pressure is very great, since now the heart is no longer slowed by 

 the vagus stimulation brought by the excess of the carbon dioxide in 

 the blood. 



DEMONSTRATION No. 4. 

 The Mechanism of Glandular Secretion. 

 A. Salivary Secretion. 



The animal is anesthetized and prepared as in demonstration No. 1. 

 An incision is made along the internal border of the jaw bone. The 

 internal border of the digastric muscle is thus exposed. This is pulled 

 aside by a hook so as to expose the transverse fibers of the mylohyoid 

 muscles. The mylohyoid is carefully severed following the line of 

 the digastric muscle. The edges are pulled to one side and the lingual 

 nerve is seen emerging from under the ramus of the jaw. In its trans- 

 verse course to the middle of the jaw, it crosses the ducts of the sub- 

 maxillary and sublingual glands. Where it crosses the ducts it gives 

 off a small branch, the chorda tympani. A ligature is placed beneath 



