with chloralosane or uretliane, the two common carotid arteries' are cut between ligatures. The thyroid vI arteries and the efferent branches of the sinus caroticus (external carotids, internal carotids, occipital, laryngeal and lingual arteries) are tied, care being taken not to sever the sinus innervation. The cephalic ends of the/__ common carotids are connected with 3 the Dale-Schuster (16) pump; outflow cannulas are placed in the Fig. 1. Showing the method of sinus efferent branches of the lingual perfusion of the two isolated sinus caroticus. arteries. Bymeans of thistechnique, which is an adaptation of the method of perfusion of the isolated sinus caroticus which one of us described before (14, 17), the two isolated sinus caroticus (bifurcation of the common carotid and ganglion caroticum), connected with the animal only by the sinus innervation, are perfused under pulsating arterial pressure with defibrinated blood or Ringer solution of which one can modify the pressure, the flow, the pulsating rate and the physico-chemical properties. The dog's respiratory rate and volume, the heart frequency and femoral blood-pressure are registered.

The two sinus caroticus being perfused at a low pressure of 60 mm. Hg (SP Fig. 2), the respiratory rate of the vagotomized dog is 28 movements per minute (R. Fig. 2). At ta, Fig. 2, a rise of the sinus perfusion pressure to 300 mm. Hg produces an immediate cessation of respiration, a reflex apncea, with a diminution of the general and cerebral arterial (vertebral arteries) blood-pressure from260 to 120 mm. Hg. This apncea remains till the moment the sinus perfusion pressure is