32 EXPERIMENTAL GENERAL PHYSIOLOGY. 



such a way as to bring the dorsum of the frog toward the palm of 

 the hand. 



(2) With the thumb and index finger grasp the frog's nose and 

 press it ventrally. 



(3) Place the point of a narrow-bladed scalpel in the median 

 dorsal line over the space between the occiput and atlas i. e., over 

 the occipito-atlantal membrane. This point is most readily located 

 by using the eyes as a landmark. 



The occipito-atlantal membrane lies at the apex of an equilateral 

 triangle whose base has its extremities in the center of the cornese 

 and whose apex extends posteriorly. Having located the point of 

 incision, press the knife through the skin, the intervening connective 

 tissue and the occipito-atlantal membrane, and cut the spinal cord 

 transversely. 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 contents of the cranial cavity may be functionally destroyed. 

 When it is required simply to pith a frog it is understood that the 

 operation is complete as described above. It may, however, fre- 

 quently be necessary to destroy the spinal cord as well as the brain. 

 To accomplish this insert the needle as described under (4); but 

 turn the point of the probe so that it shall enter the neutral canal 

 of the vertebrae. Pass it along this canal to a point nearly opposite 

 the anterior end of the ilia. Withdraw the probe. 



A pithed frog can suffer 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 destroy its spinal cord, pin it to a frog board, with 

 dorsum down and legs extended. 



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 

 stronger scissors sever the whole floor of the mouth transversely 

 and as far posteriorly as possible. Divide the skin in the median 

 line as far posteriorly as the pubes. 



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

 the median sternal cartilage and carry the incision through the 

 xiphoid appendix and abdominal walls. Withdraw the pins which 

 fix the anterior extremities ; separate the lateral halves of the sternum 

 by lateral traction upon the anterior limbs. 



(3) With the forceps grasp a fold of the mucous membrane which 

 surrounds the puckered anterior end of the oesophagus. While 

 making gentle traction with the forceps make, with fine scissors, 

 a circular incision through the mucous membrane surrounding the 

 opening of the oesophagus. 



(4) Grasp the pyloric end of the stomach, sever the duodenum, 





