LABORATORY MANUAL OF PHYSIOLOGY. 



4. While observing the capillary flow, stimulate the cut end of 

 the cord with a weak tetanizing current. What is the effect on the 

 calibre of the blood-vessels ? What conclusion can you draw con- 

 cerning the function of the cord as a conductor of vasomotor im- 

 pulses ? 



5. Cord Centres. Allow the frog to rest for ten or fifteen min- 

 utes, making an observation of the web at frequent intervals. Is 

 there any diminution in speed of flow? Is there any resumption 

 of vasomotor tone? If so, what conclusion can you draw con- 

 cerning the cord as a vasomotor centre ? 



6. Destruction of the Cord. Expose the heart and vessels 

 of the mesentery. Note the complete filling of the heart at each 

 diastole and the size of the mesenteric vessels. Now insert a 

 seeker into the spinal canal, destroying the cord. What is the 

 effect on the filling of the heart and the abdominal vessels ? What 

 disturbance of the vasomotor mechanism has occurred through 

 the destruction of the cord ? 



Examine the web. How does it compare with the condition 

 which prevailed before the destruction of the cord ? 



7. Vasomotor Centres Outside of the Cord. Pith another 

 frog, but do not destroy the cord. Wait five minutes for the vaso- 

 motor tone to be re-established. Examine the web and note the 

 size of the vessels and speed of flow. 



Destroy the cord in the same way as before and note the change 

 in the web flow. Observe the web at short intervals, for fifteen to 

 twenty minutes, or longer if necessary. Is there any return of 

 vascular tonus? Explain. 



8. Vasomotor Reflexes. Lightly curarize a frog. Carefully 

 isolate the sciatic nerve of one thigh. Examine the blood-flow 

 through the web of the opposite foot. Cut the nerve. Is there any 

 effect on the capillary flow through the web ? Is this effect con- 

 strictor or dilator? 



After five minutes, stimulate the central end of the cut nerve with 

 a weak tetanizing current. What is the result on the circulation 

 through the web ? 



[112] . 



