higher water plants and algæ 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.
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 estimation 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
