66 THE CIRCULATING LIQUIDS OF THE BODY 



(6) Acidulate some serum with dilute acetic acid and boil. Filtei 

 off the coagulum, and to the nitrate add silver nitrate. A non-protein 

 precipitate insoluble in nitric acid, but soluble in ammonia, indicates 

 the presence of chlorides. 



7. Action of Serum on Artery Rings. Cut a number of rings about 

 ij millimetres wide from a fresh carotid artery of the sheep, obtained 

 from the slaughter-house. Keep the rings in a dish in Ringer's solu- 

 tion.* They should be as nearly as possible of uniform width. A small 

 cylindrical glass vessel is supported on a stand in such a way that it 

 can be easily lowered into a bath of water kept at a temperature of 

 about 39 to 40. A stock of Ringer's solution is kept in a beaker 

 or bottle immersed in the bath. A ring of the artery is put into the 

 small cylinder, where it is held between two aluminium hooks, one 

 fastened to the bottom of the cylinder, the other (the upper one) con- 

 nected with the short arm of a lever, the long arm of which is arranged 

 to write on a slowly revolving drum. A time-trace, say in half- 

 minutes, is recorded below. The small cylinder is now filled with 

 warm Ringer's solution and lowered into the bath. Oxygen is bubbled 

 through the solution by means of a side-tube near the bottom of the 

 cylindrical vessel. The artery ring is now stretched for five minutes 

 by a weight of 10 grammes attached to the long arm of the lever at the 

 same distance from the axis as that at which the ring is attached. 

 After the stretching period the weight is removed, and a little time 

 allowed to elapse till the writing-point traces a horizontal line on the 

 drum. 'Then a bent pipette is filled with serum already heated to bath 

 temperature in a vessel immersed in the bath. The pipette is intro- 

 duced into the small cylinder so that its point is at the bottom, without 

 disturbing the ring, and the serum is allowed to run in till the Ringer 

 solution is displaced. The ring shortens under the influence of the con- 

 strictor substance in the serum, and the tracing is continued till the 

 shortening has reached its maximum and the trace is again horizontal 

 (Fig. 3, p. 46). 



Various dilutions of the serum are now made with Ringer's solution, 

 and the greatest dilution in which the serum will still cause a percep- 

 tible constriction of the rings is determined. This affords a measure 

 of comparison with other sera of the strength of the constrictor action. 

 For each dilution of serum a separate ring must be used. It must be 

 remembered that comparisons of this kind can only be made with 

 arteries of the same sensitiveness, and different arteries vary much in 

 this regard. 



8. Comparison of the Action of Serum and Adrenalin (Epinephrin) on 

 Artery Rings. Tracings showing the effect of various dilutions of 

 adrenalin chloride on artery rings may now be taken for comparison 

 with the serum effects. The adrenalin dilutions should be made just 

 before use, as adrenalin is rapidly oxidized. Or a separate experiment 

 on the action of adrenalin may be made under ' Circulation,' as on 

 p. 214. ^ 



g. Comparison of the Action of Serum and Plasma on Artery Rings. 

 Citrate plasma is obtained as follows: A cannula and attached rubber 

 tube are boiled, oiled inside with fresh olive-oil, and filled with a citrate 



* This is the name given to a solution containing the most important of 

 the inorganic constituents of blood -serum in approximately the normal pro- 

 portions. The various ' Ringer's solutions ' used by different workers have 

 varied slightly. That recommended by Locke (for perfusion of the isolated 

 heart) contains NaCl, 0-9 per cent.; KC1, 0*042 per cent.; CaCl 2 , 0*024 P er cent.; 

 NaHCO 3 , o-oi to 0-03 per cent.; with in addition o'i per cent, of dextrose, 

 which can be omitted for such experiments as 7. 



