PREFACE BY TRANSLATOR. XI 



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, arid yet 

 be a mere tyro with the microscope. When, then, we 

 see it announced that Dr. So-and-so failed to discover 

 any micrococci 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 which 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- 

 micrographs 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 



