1052 The American Naturalist. [December, 
sies in the biology of this imperfectly understood group. 
Beyerinck applied the gelatin method in the isolation of alge 
and succeeded in cultivating a number of free unicellular 
forms, some symbiotic species in certain hydra and parame- 
cia, and a number of the gonidia in lichens. So far all 
attempts to apply the isolation methods of solid media to ani- 
mal life have proven futile. Strenuous efforts have been made 
‘upon such parasitic forms as the malaria plasmodium 
and other parasitic protozoa, but as yet these experiments 
have not been successful. 
With respect to tinctorial methods, bacteriology has been 
of service. The art of staining to bring out structural differ- 
ences more clearly has been systematically developed in the 
latter half of the present century. The discovery of aniline 
colors in the seventies gave an additional impulse and the 
names of Koch, Ehrlich, and Weigert will always be associa- 
ted with the rapid advance and development of this branch of 
biological technique. The necessity of staining in order to 
differentiate bacteria in animal tissue has been so imperative, 
that much time and effort have been expended in order to 
improve the old, and discover new processes. The success of 
these efforts has been stimulating in other lines of work, and 
has materially advanced the general knowledge of stains. 
Koch in 1878, was one of the first to apply photography to 
the study of microscopic preparations. The application of this 
process by means of photograms for class demonstration, and 
the obvious advantages that it possesses for accurate illustra- 
tionareapparent. The recently completed photomicrographic 
atlas of bacteria by Friinkel and Pfeiffer exemplifies the degree 
of excellence that has already been attained in this branch. 
In the study of bacterial forms, the old types of microscopes 
were entirely inadequate. The necessity of improved instru- 
ments, in regard to definition and resolution to work out the 
structure of these “infinitely little” organisms, acted asa 
. healthy stimulus on the art and science of lens making. The 
perfected instrument of to-day, with its homogeneous immer- 
sion, the Abbe condenser, and the apochromatic objective, are 
largely the result of the demand of bacteriologists. These 
