98 THE MICROSCOPE. [April, 



rapher — thick preparations for the one and thin for the other ; 

 less expenses and not such accurate results. When slides are 

 scarce and valuable their usefulness may be duplicated by nega- 

 tives. In drawing we have the satisfaction of showing the ideal 

 tissue or point of discussion or illustration. The draughtsman 

 can, by simply focussing the micrometer screw, combine the dif- 

 ferent planes in one and reproduce the regularity of the specimen. 

 This in photomicrographv is impossible. All this is why there 

 are errors and misinterpretations and abuse of this art. It is in 

 the study of micro-organisms, where, if ever, a pure objective 

 perception, free from every preconceived idea, is necessary, for no 

 one will deny that the difterence in conception of the character- 

 istics of one and the same object almost always depends upon the 

 fact that the object appeared to the one observer under a different 

 form from that to which it was seen by a second. A slight 

 movement of the adjustment screw will cause a delicate object to 

 disappear entirely from the field, or to appear with different 

 markings and shadows. Results are always aided by the use of 

 the microscope apparatus, light, and magnifying power, but if the 

 conditions under which the objects are seen be different in the 

 matter, say of the size of diaphragms, high or low eye-piece, etc., 

 or if the staining or the mounting of the objects be dissimilar, 

 how can we W'Onder at the varieties of opinion. To do awa}' 

 with these variations, which in microscopy frequently have been 

 proved to exercise a most injurious influence on the progress of 

 knowledge, there is only one remedy, and that is photography. 

 It comes as a harmonizing mediator. Under some circumstances 

 the picture is more valuable than the original object. If we give 

 some one a microscopical preparation with the view to his exam- 

 ining some particular sjDot in it, for instance, a lymph vessel con- 

 taining bacteria, we do not know whether he will find the right 

 place in it, or if he does see it whether he will have selected 

 proper focus or the best illumination, etc. Several observers can 

 come to a conclusion very quickly by using the photograph, while 

 the object can be accessible to only one person at a time. It is 

 easy to point out the object ; measure it with compasses, compare 

 with other photographs similarly taken, whether of the same or 

 of other specimens. In photography the microscopist exercises 

 a powerful control over his own observations. 



Microscopical drawings of specimens are rarely absolutely true 

 to nature ; they are prettier and appear with sharper lines and 

 stronger shadows than the original, and, as happens not unfre- 

 quently, a sharper line or darker shadow in particular places may 

 give the figure quite another signification. The drawing, further, 

 is no clue to the value of the preparation, for even a badly pre- 

 pared and in itself a doubtful specimen may be represented by a 

 beautiful and apparently convincing drav^^ing. This is impossi- 



