16 LABORATORY MANUAL FOR ELEMENTARY ZOOLOGY 



contraction. Turn the heart with the apex forward so that the sinus venosus 

 can be seen. Does the sinus beat? What time relation does its beat bear to 

 that of the auricles and ventricle? 



Count and record the number of heart beats per minute. Then cool the 

 heart by placing small pieces of ice around it, and after it has become thoroughly 

 chilled again count the rate of the heart beats. This illustrates in a striking way 

 the effect of change of temperature on the activities of living matter. 



4. Ciliary motion. Open the mouth of the frog, swab it out with water, and 

 if necessary cut the angle of the jaws to keep it open. Lay the frog ventral 

 side up and sprinkle a little powdered carmine or place small bits of cork on the 

 posterior part of the roof of the mouth. Observe that the particles travel as 

 if carried on a current. (If the experiment fails it is because the frog has been 

 pithed too long, and a fresh frog may be necessary.) The current is due to a 

 multitude of microscopic hairlike processes, called cilia, which cover the roof 

 of the mouth, and by their co-ordinated beating produce a current of mucus 

 which is sufficiently strong to carry fairly large particles. Prove that the particles 

 will be transported against the force of gravity by repeating the experiment with 

 the head of the frog tilted at an angle, so that the particles must be carried uphill. 

 In which direction does the ciliary current run and what is its purpose? While 

 the causes of ciliary motion are not at all understood, it is probable that like 

 muscular movement it is a form of contractility. 



5. Amoeboid movement. In this type of movement, which is limited tc 

 very small or microscopic masses of living matter, locomotion is accomplished 

 by the flowing out of portions of living substance into processes. The remainder 

 of the substance then flows into the processes, new processes are put out, and a 

 slow change of position is thus effected. Amoeboid movement is probably the 

 most simple form of contractility, but an adequate analysis of its causes has not 

 yet been made. 



Amoeboid movement is illustrated in the frog in the black chromatophores 

 or color bodies of the skin, and in the white blood corpuscles, both of which objects 

 will be seen later. For the present see Holmes (Fig. 49, p. 189, and Fig. 71, 

 p. 259), as neither of them is very favorable for the study of this kind of move- 

 ment. Amoeboid movement will be studied in the amoeba, the animal from 

 which the movement takes its name. 



C. FUNCTION OF THE DIGESTIVE SYSTEM; DIGESTION, ABSORPTION 



The food of animals in general consists of water, salts, and organic substances, 

 these latter being divided into three classes, proteins, carbohydrates, and fats. 

 Examples of proteins are meat, white of egg, curdle of milk, blood clot; sugars 

 and starches are carbohydrates; butter, fat of meat, cream, are examples of fats. 

 While the water and salts pass into the substance of the animal without alter a- 



