144 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



furnish fresh air to the living low forms of life. They will invariably 

 seek the bevelled edge of the cavity, and so are in the reach of the 



Fig. 27. 



highest powers. Owing to the supply of fresh air, the living animal- 

 cule may (it is said) be kept for weeks. It is adapted, too, for 

 studying the circulation of the blood in the tail of the tadpole. 



(2) " Life and Current Slide." — In a slip of plate-glass (Fig. 28), two 

 oval cells are ground and polished, which are connected by a very 

 shallow channel. If the cells are partly filled with blood and covered 

 by a thin cover-glass, the expansion of the air in one cavity will drive 



Fig. 28. 



the blood through the channel, and then it may be observed under the 

 most favourable condition, even for a high power. The apparatus is 

 so sensitive that the current may be changed by bringing the finger 

 near one of the cavities, and arrested by moving the finger away. 



(3) " Siplion Slide."— This (Fig. 29) consists of a slip of thick 

 plate glass, with two shallow oval cavities and a deep groove in the 

 middle, to hold a small fish or Triton, and retain it without undue 

 pressure in a fixed position. Small metallic tubes communicate with 

 the extremity of the deep groove. Rubber tubes are connected with 

 these metal tubes, one of these being intended for the entrance and the 

 other for the exit of any fluid, cold or hot. When in use it is only 

 necessary to place the animal with some water into the groove, cover 

 it with the glass cover, immerse one of the rubber tubes in a jar of 

 water, and, by suction, draw the water through the apparatus. If the 

 slide is placed on the stage of a Microscope the jars should stand lower, 



