422 PHYSIOLOGY OF GROWTH. 



lamp by an oil float-lamp, such as is represented in the figure, and 

 wait till the temperature becomes constant. To get higher or lower 

 temperatures, it is sufficient to put into the lamp one, two, or three 

 floats with night-lights. To make observations at low tempera- 

 tures, it is merely necessary to put into the water in the box from 

 time to time fragments of ice. It is very desirable to wrap the 

 part of the microscope projecting from the case with cotton wool, 

 so as to eliminate as far as possible sources of error. 



In accurate researches as to the influence of temperature on 

 protoplasmic movement, it is necessary to determine the time 

 taken by some constituent of the cell, e.g. a chlorophyll grain, in 

 passing at a particular temperature from one edge of the field of 

 view across the middle to the other edge. We may also determine 

 the time required by a chlorophyll grain to traverse the longi- 

 tudinal wall of a cell not extending across the entire field of view. 



It is to be observed, 

 1 ^jf ""HI ' +- ^~*** that in judging the 



rate of movement, we 



Fi. 138.-Gas chamber for employment in micro- , attention to 



scopical researches (represented in section). J r > 



chlorophyll bodies 

 whose movement is free and undisturbed by others. 



To prove the important fact that want of free Oxygen arrests 

 the movement of the protoplasm, it is very convenient to employ 

 a gas chamber such as that represented in Fig. 138, and obtain- 

 able from Albrecht, Tubingen, at a price of 15 mks. It is about 7 

 cm. long, 4'5 cm. broad, and 5 mm. high, and is made of metal. 

 At the bottom is cemented air-tight a rather large sheet of glass ; 

 at the top is a circular opening. Over this is laid the cover-glass, 

 from which hangs a drop of fluid carrying the material to be 

 observed. The bottom of the chamber is moistened with a thin 

 layer of boiled-out water, to prevent the research material from 

 getting dried up. The cover-glass can readily be fixed air-tight by 

 means of fat. The tubes _K and R' serve to lead gas to and 

 from the preparation. The Hydrogen which is to be employed is 

 prepared and purified in the manner described in 160. The gas 

 chamber is placed on the stage of the microscope. We select for 

 examination say staminal hairs of Tradescantia, or hairs from the 

 young leaf-stalk of Cucurbita Pepo. It is also convenient to experi- 

 ment with infusoria. We easily obtain them by flooding hay with 

 water, and allowing to stand for about eight days. The fluid then 

 contains chiefly numbers of Paramecia, whose elongated bodies 



