EXPERIMENTAL BIOL GY 



593 



and sterilizing flames. One line of research is to subject organisms to 

 the influence of different densities in the surrounding medium. For 

 fluids there are basins containing different concentrations of salts, 

 brackish water, etc., •with an areometer for measuring the specific grav- 

 ity of each of the various liquids. For gases there are hand air pumps 

 and means of attachment to the supply pipes of the large electric air- 

 pump located in the cellar. For changing the normal influence of 

 gravitation there are clinostats regulated by clockwork and centrifuges 

 with contact plugs for tapping the electric power wherever needed. 



Two dark rooms (Fig. 11) are fitted for studying the influence of 

 light. Both open into a dark corridor from which a triangular door 



Fig. 10. The Phtsico-chejiicax Labobatoet. 



leads into an anteroom lighted by a red dark-room light. The larger 

 dark room serves for investigations upon the influence of definitely 

 determined lights. Hung up at one end is an arc lamp in which dif- 

 ferent colored carbons can be used. The elongated form of the room 

 makes possible experiments in which the organisms are placed at dif- 

 ferent distances from the light source. For investigating the influence 

 of variously colored surroundings, small vivaria are placed in lighted 

 rooms with colored glass covers for direct light, or colored wall cover- 

 ings, for reflected light. A special apparatus has been constructed for 

 the study of under and over lighting of fishes and amphibia (Fig. 12). 

 For over lighting the aquarium is covered with an enclosing box open 

 above (o) and for under lighting the box is closed above (u). For in- 



