ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



603 



allowing the ball to expand fluid is sucked up past the valve (b). On 

 repeating this operation two or three times the air is driven out and the 

 whole of the apparatus is filled with the fluid. The ball is then 

 compressed by means of the board, and the position of the screw (c) is 

 found which results in the delivery of the desired amount. Delivery 

 should be made by an even pressure applied as uniformly as possible. 

 It is important to keep the length of the rubber tubing as short as 

 possible and to use thick-walled pressure tubing. Under these 

 conditions the volume delivered is almost independent of the rate of 

 compression of the ball. 



Fig. 38. 



Handling Protozoa in Pure Line Work.* — During the past year 

 R. T. Hance has been engaged in experiments on the inheritance of 

 extra contractile vacuoles in a new race of Paramoecium, and has 

 worked out some methods of technique that have much facilitated his 

 work, e.g. maintaining pure cultures. The greatest care is necessary to 

 prevent pure line cultures from becoming mixed with others. Even 

 with labelled pipettes accidents may occur. The scheme shown (fig. 39) 

 was recently devised and has proved most convenient. A piece of soft 

 brass wire is shaped about some round object of a diameter slightly 

 larger than a pipette, and is held by several twists. Then the long 

 ends of tlie wire are bent around the culture jar and again fastened by 

 twisting the ends. In the jars used there is a convenient groove near 

 the top into which the wire fits nicely. When finished the small circle 



* Trans. Amer. Micr. Soc, xxxv. (1916) pp. 135-6 (1 fig.). 



2x2 



