CURRENT LITERATURE 
BOOK REVIEWS 
An encyclopedia of microscopical technique 
In the exact sciences, as a rule, the formulation of a working hypothesis 
precedes the discovery of methods for its investigation. In biology, on the 
other hand, this procedure has been often reversed, for here we frequently 
find that the whole aspect of a science has been changed as a result of new 
facts brought to light by methods which have been empirically developed. 
For example, no one could have foreseen that, if nervous tissues were treated 
successively with solutions of potassium bichromate and silver nitrate, the 
resulting precipitate of silver chromate would be deposited almost exclusively 
on the nerve cells and their processes; nor that the medullary sheaths of nerves 
after long treatment with potassium bichromate would stain strongly in 
hematoxylin. Yet these two methods have, to a large extent, made pos- 
sible the modern science of neurolo ogy. 
The fact that the element of chance has played so large a part in the de- 
velopment of methods for microscopic investigation is doubtless due in part to 
the lack of adequate training in chemistry and physics of those engaged in 
microscopical investigation,-and to the lack of interest in microscopical struc- 
tures of those possessing this training; but it is also due in part to the fact that 
our texthooks of microscopical technique have, for the most part, described 
the technical manipulations simply as routines to be followed to attain certain 
results, assuming that the individual using them did not need to know the 
nature of the reagents he was using, why they were used, nor what each con- 
tributed to the final result. 
It is sometimes true that careful adherence to an established routine is the 
safer course for persons of certain limitations in training, but such persons 
are necessarily limited in their investigative outlook to the exploitation of new 
material by means of old methods, or to the uncertain hazard of the accidental 
discovery of new methods. The road to the discovery of new investigative 
methods by intelligent and well planned experiments is open only to those who 
are equipped with a knowledge of the chemical and physical properties of the 
materials with which they are dealing. In this field of experimentation the 
textbooks of microscopical technique, with one exception, give us but little 
help. The exception is MANN’s Textbook of physiological histology, in which the 
problems of fixation and staining are fully discussed from the standpoint of 
the chemistry of the organic materials under investigation, and of the reagents 
employed. In this work, however, the limitations of theme and space pre- 
vented the general application of this method of treatment to the whole field 
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