EXPERIMENTAL BIOLOGY 



595 



vironment so that different plants and animals can be observed during 

 several generations at specified and perfectly controlled temperatures. 

 Four rooms are kept at + 5° 0., + 10° C, + 15° C. and + 20° C. 

 The carbonic acid machine (Fig. 14) produces 5,500 calories hourly. 



Fig. 12. Apparatus for Over and Under Lighting, d, compressed air ; s, mirror ; 

 o, box, open above ; p, box, open below ; w, glass walls. 



The fluid carbonic acid flows into a wrought-iron spiral core within a 

 carefully isolated receptacle made of tin plate. The salt water sur- 

 rounding the spiral core is cooled to a low temperature by the sudden 



Fig. 13. Warm Room with Compartment for Elevated Temperature 



on the Right. 



expansion of the liquid carbon dioxid. Then the carbonic acid gas is 

 compressed under 55 atmospheres and conducted into a wrought-iron 

 spiral core in the condenser where it is again cooled, liquefied and 

 ready to flow on in the continuous circulation through the machine. 



