GENERAL PHYSIOLOGY. 17 



knife through the skin, the intervening connective 

 tissue and the occipito-atlantal membrane, and^cut 

 the spinal cord transverely. Withdraw the knife. 

 (4) Insert the apex of a slender probe or of a blunt 

 needle into the incision, turning it sharply forward 

 so as to enter the cranial cavity. By sweeping the 

 distal end of the probe from side to side the con- 

 tents of the cranial cavity may be functionally de- 

 stroyed. When it is required simply to pith a frog 

 it is understood that the operation is complete as 

 described above. It may, however, frequently be 

 necessary to destroy the spinal cord as well as the 

 brain. To accomplish this insert the needle as de- 

 scribed under (4) ; but turn the point of the probe 

 so that it shall enter the neural canal of the verte- 

 brae. Pass it along this canal to a point nearly op- 

 posite the anterior end of the ilia. Withdraw the 

 probe. 



A pithed frog can surfer no pain, but will respond 

 reflexly to certain stimuli. A pithed frog whose 

 spinal cord is destroyed cannot with the skeletal 

 muscles respond reflexly to any stimuli. Having 

 pithed the frog and destroyed its spinal cord, pin it 

 to a frog board with dorsum down, and legs ex- 

 tended. 

 To remove the (Esophagus of a frog. 



(1) Place the head of the frog nearer to the operator. 

 With forceps lift the mandible and with the stronger 

 scissors sever the whole floor of the mouth trans- 

 versely and as far posteriorly as possible. Divide 

 the skin in the median line afi far posteriorly as the 

 pubes. 



(2) Separate the two lateral halves of the sternum by 

 dividing the median sternal cartilage and carry the 



