PRACTICAL EXERCISES 447 



head. The small intestine is immediately removed. It may be cut 

 between double ligatures into several pieces for this purpose. The 

 contents are rapidly washed out by a stream of warm Ringer, and 

 the pieces placed in (b), through which oxygen is kept bubbling. The 

 pieces are conveniently supported in the liquid by threads fixed by 

 the cork of the bottle. There is a hole in the cork for the escape of 

 the oxygen. The movements of the intestines in (b) can be studied 

 very well by inspection. Or a separate length of intestine maybe kept 

 for this purpose, the contents not being removed, but prevented from 

 escaping by ligatures at each end. This can be most easily observed in a 

 shallow dish of warm Ringer. Or a separate experiment can be ma,de 

 in which the whole alimentary canal of a rabbit is carefully removed 

 and examined in oxygenated Ringer's solution. 



A segment of intestine about 2 or 2^- cm. in length is now cut off 

 one of the pieces. A small ring of platinum or aluminium is tied to 

 a point on the circumference of one end of the preparation by a silk 

 thread passed through the wall. The other end is caught by a serre- 

 fine at a point exactly corresponding to the attachment of the ring, so; 

 that the pull of the contracting longitudinal muscle should be in the ; 

 straight line joining these two points. The serre-fine has attached to 

 it a thread with a hook on the other end. In preparing the intestinal 

 segment it lies on a plate of glass above a vessel of warm water. The 

 small cylinder (c) is now partially filled with warm Ringer's solution. 

 The ring is grasped by fine forceps, and made to engage with the hook 

 at the bottom of the cylinder, care being taken not to injure the prepara- 

 tion in the process. The cylinder is then fastened on its stand and 

 lowered into the bath. The thread is connected by its attached hook 

 to the lever, and oxygen allowed to bubble slowly and regularly through 

 the cylinder. Very soon rhythmical contractions begin (Fig. 173), and 

 continue for a long time. The effect on these contractions of abolish- 

 ing, reducing, or increasing the oxygen-supply may first be studied. 



2. Effect of Blood-Serum on the Contractions of Intestinal Segments. 

 While a tracing is being taken as in i, fill a small bent pipette with 

 serum already warmed in the bath, pass the point of the pipette down to 

 the bottom of the cylinder without interfering with the preparation, and 

 allow the serum to flow in till the Ringer's solution is displaced. Almost 

 at once the lever will begin to rise, indicating strong tonic contraction. 

 The increase of tone lasts for some time, but can soon be removed on 

 washing the preparation with Ringer. This is most easily done, while the 

 drum is stopped, by introducing pipetteful after pipetteful of Ringer's 

 solution into the cylinder in the way described, allowing the liquid to 

 overflow into the bath. The subsequent addition of serum causes a 

 renewed increase of tone, and this may be many times repeated. 



Determine the greatest dilution of the serum which still produces a 

 distinct effect upon the intestinal segment. 



3. Action of Epinephrin (Adrenalin) on Intestinal Segments. Pro- 

 ceed as in 2, but use various dilutions of adrenalin chloride instead of 

 serum. They must be freshly prepared. Instead of increase of tone, 

 inhibition of the movements and decrease of tone will be obtained 

 (Fig. 173). 



This experiment may be performed at another stage in the course 



(P- 693)- 



4. Quantitative Estimation of Ferment Action. For pepsin an easy 

 method, although not a very accurate one, of estimating the rate at 

 which the fibrin disappears is to use fibrin stained with carmine. As 

 solution goes on, the dye colours the liquid more and more deeply, and 

 by comparing the depth of colour at any tim3 with standard solutions 

 of carmine, we get the quantity of dye set free, and therefore of fibrin 



