64 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



forward and at one side under the bony covering of cerebrum and snip 

 the bone. Repeat on other side. Raise the bone with small forceps and 

 carefully cut forward, alternately on one side and the other, until cerebrum 

 is exposed. Sever connections between optic lobes and cerebrum and 

 remove it. Sew together flaps of skin with silk thread moistened with 

 antiseptic Ringer. 



Note posture. Keep animal 1 hour in moist container and then com- 

 pare with normal and spinal frog (whole brain pithed) as follows: (a) 

 Record differences in Posture, Locomotion (Hopping and Swimming) and 

 Respiration, (b) Vision. Compare eyelid movements. Stimulate frog 

 to jump toward an obstacle 6 cm. distant in path of light beam, (c) 

 Equilibration. Turn frog on its back. Compare reactions. Slowly tilt 

 support of frog in normal position, (d) Croak reflex. Hold frog imme- 

 diately behind front limbs. Apply temporary light pressure, (e) 

 Nystagmus. Place the animal on rotating surface (phonograph or card- 

 board mounted on kymograph shaft). Note head movements. 



If the operation is successful the frog should be kept for several days (in 

 moist chamber) and tested again. Label the jar with your name and the 

 date. For effects of decerebration on the frog cf. Mitchell, 1932, p. 145. 



XI. PERMEABILITY AND OSMOTIC PRESSURE OF LIVING CELLS 



The irritability of living cells as seen in the muscle and nerve experi- 

 ments (above) is largely determined by the permeability of the plasma 

 membrane which will be studied in the following experiments. 



1. Membrane of Oxide on MetaL — Place a large globule of clean Hg 

 into a watch glass of distilled water and another of the same size into a 

 watch glass of 10% hydrogen peroxide. Stir each with a blunt point to 

 separate into smaller drops. Note differences. With the blunt point 

 gather the drops together again. Explain isolation of drops in H2O2. 

 Gently tip the watch glass containing a large globule of Hg in H2O2. 

 Observe oxide membrane on upper side (Lillie, "Protoplasmic Action," 

 1932, p. 247). 



2. Iron Wire Model of Plasma Membrane of Nerve Fibre. — An iron 

 wire covered with a film of oxide in nitric acid transmits an electrical 

 "action current" resembling the nerve impulse. Touch the end of the 

 iron wire in the demonstration with a Zn rod (why?) and observe the 

 propagated disturbance indicated by bubbles. The "nerve" must be 

 allowed to rest during the refractory period (rebuilding of film) after 

 each stimulation (cf. Ponder, "Gen. Physiol.," p. 269, or Lillie, "Proto- 

 plasmic Action," 1932, p. 254; Biol. Reviews, 11 : 181, 1936). Text p. 196. 



3. Permeability Changes during Stimulation. — Place Spirogyra fila- 

 ments on a slide with pond water stained with acid fuchsin. By means of 

 tin foil electrodes, stimulate with a weak interrupted current and observe 



