EXPERIMENTAL BIOLOGY 



59i 



higher water plants and algae which grow during the warm season. 

 In the shady, western part of the garden there are six cement basins 

 (Fig. 9), especially for the rearing of plants, and at the same time 

 serving as a home for the hosts of protozoa that wander in and can be 

 used for investigations. 



A station for experimental biology must have not only the proper 

 equipment for breeding and rearing organisms under natural conditions, 

 but also for artificially changing and controlling the external factors of 

 the environment. The physico-chemical laboratory (Fig. 10) provides 

 the substances used as variable external factors and also to determine 

 the physico-chemical properties of the biologically important colloids. 



Fig. 8. Large Basin in front of the House for Higher Vertebrates. 



These albuminous substances are placed in parchment paper sacks, in 

 closed vessels or in moving water from which the carbon dioxid has 

 been removed and thus for weeks and months are kept free from decay 

 or carbon dioxid or other noxiousness of the laboratory air. A heliostat 

 provides for the penetration of objects with the rays of sunlight and 

 for the ultra-microscopic ends. A nephelometer is used for the estima- 

 tion of cloudiness whereby errors in physiological observation due to the 

 confounding of comparative and observation fluidities may be reduced. 

 A dilatometer serves to determine the changes in volume and variations 

 in water content of the biocolloids. Then there are pycnometers of all 

 kinds for specific gravity computations and an Ostwald's viscosimeter, 

 in a transparent thermostat, for the determination of the viscosity of 



