8 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



drop of culture medium containing Paramecium and later examine the 

 tubes under the microscope or with a large reading glass for Paramecia. 

 Make sure that there are no air bubbles at the tips of capillary tubes. 

 The tubes may be held with plasticine at the edge of the culture 

 fluid. Cover to prevent evaporation (cf. Loeb, "Forced Movements," 

 pp. 144-146, 1918). 



16. Geotropism (Orientation by Gravity) in Ants. — With a soft pencil 

 carefully trace the path followed by an ant crawling over a sheet of paper 

 on a glass plate tilted at 5°, 25°, 45°, 80°, etc. from the horizontal; 5-10 

 trails at each inclination should be recorded. The angle of orientation 

 (0) is that between the path and the transverse axis of the plane. Plot 

 mean angles of orientation against sine a(jcx = angle of tilt of the plane). 



Fig. 2. — Method of handling ants and other small animals. 



Ants must be handled with great care by means of two small paper squares 

 on which the ant crawls and is placed on the plane (see Fig. 2). At low 

 a. angles random movements occur in all directions but statistically the 

 6 angles increase with the steepness of the plane. Cf. Barnes, J. Gen. 

 Psychol., 2: 517, 1929. 



17. Phototropism in Limax. — Place a slug with one eye removed (on 

 the previous day) on a moist plate under bright overhead illumination. 

 Observe the circus movement. To which side does the animal turn? 

 Explain. Animals must be kept in the dark immediately prior to experi- 

 ment (cf. Crozier in Murchison's "Handbook of General Experimental 

 Psychology," p. 12, 1934). 



18. Orientation between Opposing Beams of Light. — Allow a meal 

 worm or pill bug to crawl between two lights set up in a special dark 

 room. Record the paths of orientation at various distances between the 

 lights. With an illuminometer calibrate the distance in centimeters 



