88 ELEMENTARY PHYSIOLOGY. XVI. 



of venous pressure, and the appearance of pulse waves 

 on the venous side. 



5. Open M and N and observe the flow from the 

 tubes, and that the suction of the pump draws air into 

 the system through the venous tube. In the body the 

 heart does not act in this way, but inspiration does. 



6. Examine the circulation in the frog's web which is 

 placed under the microscope. The frog has had its brain 

 destroyed, and has been curarised. The sciatic nerve has 

 been tied and cut. Stimulate the peripheral end of the 

 sciatic for a few seconds with a tetanising current ; note 

 the contraction of the arteries causing slowing or com- 

 plete cessation of the circulation. 



DEMONSTRATIONS. 



1. Action of valves in a large vein. 



2. The effects in the rabbit on the temperature of the 

 ear, and on the calibre of its blood vessels, following 



a. Section of the sympathetic nerve in the neck. 



b. Stimulation of the peripheral erfd of the sympa- 

 thetic. 



3. Normal kymographic tracings of the blood pres- 

 sure of a 'mammal obtained by the use of a mercurial 

 manometer. 



4. The effects on the arterial blood pressure, as indi- 

 cated by the tracing, produced by 



a. Inhibition of the heart through stimulation of the 

 peripheral end of the vagus. 



b. Dilatation of the small blood vessels through 

 stimulation of the central end of the depressor nerve. 



