224 INTRODUCTION TO GENERAL PHYSIOLOGY 



calcium are required to maintain normal beats. This is Ringer's 

 solution. (See P, p. 209). 



Make the Ringer's solution just acid to methyl-red (io~ 4 N in 

 H-ion) and perfuse. On the other side, make it alkaline to phenol- 

 phthalein (icr 9 ) and perfuse. 



Hydrogen-ion Regulation. Make a solution of sodium bicarbonate 

 of 0.25 per cent., which is about the usual concentration in the blood. 

 Put 5 c.c. of this into a stoppered bottle, add a drop of o.i per cent, 

 neutral red. Fill the bottle with the first air expired after a deep 

 inspiration. Shake together. The colour is orange-red. Fill the 

 bottle with alveolar air (p. 176). The colour becomes red. Run in 

 carbon dioxide from a Kipp generator. The colour is crimson. 

 Replace by repeated changes of atmospheric air. The colour goes 

 back through red to orange and yellow. Bicarbonate solutions 

 lose carbon dioxide to air, becoming more and more alkaline. 

 Thus the hydrogen-ion concentration is regulated by the proportion 

 of carbon dioxide to bicarbonate. 



Vaso-Motor Effects 



Prepare a frog for observation of the circulation in the web 

 (p. 221). Carefully dissect out the sciatic nerve in the thigh, avoid- 

 ing injury to the blood vessels. Pass a thread under the nerve 

 Select an arteriole for observation, and measure its diameter by the 

 ocular micrometer. Lift up the sciatic nerve and cut it. Note the 

 widening of the arteriole. Pick up the peripheral end with forceps ; 

 tie a thread just beyond the points of the forceps. After waiting 

 a minute or two, measure the arteriole again and then stimulate 

 the nerve with induction currents of moderate strength. The 

 arteriole narrows. It may be necessary to tie down the leg or 

 pin it to the cork, owing to the muscular contractions produced by 

 the stimulation. But the better way would be to curarize the frog, 

 as described above (p. 199). 



Apply a drop of dilute adrenaline solution (i in 10,000) to the 

 web. The arteriole becomes almost obliterated. 



Take the web of the opposite side and allow a drop of a 

 saturated solution of chloroform to fall upon it. The arterioles 

 dilate, and a more copious flow through the capillaries is seen. 



Wash away the chloroform, and when the circulation has become 

 normal again, apply a drop of a solution of histamine (o. I per cent.). 

 If the dose is correct the capillaries may dilate, but not the 

 arterioles. 



Adrenaline is sold in convenient tabloids by Burroughs & 

 Wellcome, under the name of " hemisine." Histamine tabloids are 

 sold as " ergamine." 



