The pancreatic juice continues the change of starch into sugar which is commenced by the saliva, but it also digests other food-stuffs as well. Similarly, gastric juice and bile are each concerned with the digestion [Pg 235] of certain foods. The result of the action—separate and combined—of the digestive fluids is that, when a rabbit eats no more food than it requires, all the useful parts of the food are absorbed into the blood, and then distributed to the tissues by the blood as it flows through them. 46. THE CIRCULATION OF THE BLOOD. 1. Evidence of the circulation.—(a) The arterial pulse.—Feel your pulse at the wrist and count the number of beats per minute. (b) The beats of the heart.—Similarly count how many times your heart beats per minute. Put your ear over the heart of a friend, and listen to the sounds of the heart. How many different sounds can you distinguish? (c) The valves of the veins.—Press your thumb on your arm inside the elbow, and then move it down the arm towards the wrist. Notice the small knots which rise under the skin between the point of pressure and the wrist. 2. The structure of a sheep’s heart.[12]—Procure from the butcher a sheep’s heart with, if possible, the lungs still attached. If the thin transparent bag which naturally surrounds the heart has been left on, carefully cut it away. Make out the main external features of the heart before cutting into it. The shape is conical, the apex of the cone being posterior, the base (where the blood-vessels are attached) anterior. The ventral face is rounded; the dorsal face is flatter. Compare Fig. 164. The line of fat (3) marks the line of division between two chambers, the right (R.V.) and left (L.V.) ventricles. Feel that the right ventricle yields to pressure more readily than the left. Two more chambers, the right and left auricles, are situated at the basal (thick) end. R.A. and L.A. are flaps of the right and left auricles respectively. Identify the great vessels SVC and IVC which discharge into the right auricle. Cut them open to see the entrance. Then lay open the right auricle. [Pg 236] Pass your finger down and notice that the right auricle communicates freely with the right ventricle. Observe that you can from the right ventricle pass your finger into the tube P.A.; make out that this goes to the lungs. Lay open the left auricle, and see that it receives vessels from the lungs. Pass your finger from the left auricle into the left ventricle, and notice that this latter chamber leads into the Aorta, Ao. (A´o´. a branch of Ao.). Notice that the walls of the blood-vessels in connection with the two auricles are collapsed, while those (P.A. and Ao.) leading from the two ventricles are more elastic and remain open. Which of the two auricles has the thicker wall? Which of the two ventricles has the thicker wall? Can you pass your finger from one auricle to the other? From one ventricle to the