PREFACE BY TRANSLATOR. 5 
whose skill and training in the use of the microscope we 
have no means of judging. Such a man may be a great 
surgeon, or a great clinician, or a great chemist, and yet 
be a mere tyro with the microscope. When, then, we 
see it announced that Dr. So-and-so failed to discover 
any micrococct in pus, in blood, or what not, taken from 
a certain source, we are justified in asking, — first, what 
power did the learned doctor use? second, is he capa- 
ble of distinguishing micrococci in fluids whieh contain 
them beyond question? Or, if he does discover them, 
we may ask if he is accustomed to making a differential 
diagnosis between micrococci and inorganic granular 
material, or unorganized granules of organic origin. 
This is a decision which the most accomplished micro- 
scopist is sometimes unable to make, except by the aid 
of chemical tests and culture experiments. 
To avoid this want of confidence in results, which has 
naturally grown out of carelessly made observations and 
contradictory statements, it is desirable that full and 
minute details should be given of all observations and 
experiments made, and, whenever possible, that photo- 
micographs should be made of all micro-organisms 
described, or of a thin stratum of a liquid asserted not 
to contain any; as, when a sufficiently high power is 
used, this settles the question of their presence or 
absence, beyond dispute, and enables other students to 
make comparisons and measurements which cannot fail 
to promote the interests of true science. 
The National Board of Health of the United States 
has the credit of first adopting this method of recording 
the results of scientific investigation, in this direction, 
as a constant and unimpeachable record of what has 
