604 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



protrudes from the jar, and into this ring the pipette is dropped, giving 

 the appearance seen in fig. -iO. With this method pipettes are always 

 at hand and there is no danger of mixing the hnes by transferring 

 animals from one culture to another. 



Freparation of Watch-glasses. — Syracuse watch-glasses have been 

 used for single individuals throughout the work, and considerable 

 difficulty was experienced at first in locating animals which were close 

 to the edge of the container. They frequently found their way there, 

 as the fluid liad a tendency to spread evenly over the surface of the 

 watch-glass. The l)est method to obviate this was hit on accidentally. 

 There was a trace of paraffin in a pan in which the glasses were being 

 sterilized one day, and this coated the glasses imperceptibly, but 

 sufficiently to give the liquid no hold on the glass. In vessels treated 

 in this way the surface tension of the medium tends to draw it into a 



Fig. 39. 



Fig. 40. 



spherical mass. Should the liquid roll to the edge of the glass, where 

 the animals would be hidden from view, it is easily rolled out again by 

 tilting the glass, and none of the animals in the drop are left behind. 

 When animals are being kept in very small drops of water, as many as 

 twenty individual drops of liquid containing Protozoa may be placed in 

 a single watch-glass and they have not ran together. The surface 

 tension of the liquid draws it up when on a paraffined surface until it 

 gives a very fair picture of a drop of mercury. Furthermore, being 

 contracted to the smallest area possible, there is less evaporation than 

 when the same amount of fluid is spread out, and the chances of losing 

 a valuable specimen through drying are much less. The writer's 

 practice is to use a piece of paraffin about the size of a pea to a quart 

 of water. This will be sufficient for a surprising number of watch- 

 glasses. When the sterilized glasses are removed they are wiped while 

 hot and polished. Xo paraffin is visible, although a faint trace of it 

 can be felt. 



