If 



BACTERIOLOGY. 



obtained in the micro-photograph ; sujjposing, for example, in 

 the micro- pliotograph the lines which are i^jjjj inch apart are 

 delineated 1 inch apart, the magnifying power mnst be 1,000 

 diameters. Moreover, ha\ing tlins ascertained the amplification, 

 we can accurately compute from the photograph the size of the 

 objects taken. 



Vahie of Photographs. — It is not necessary to compare the 

 relative merits of diagrams and photographs. Diagrams which do 

 not purport to be accurate representations, but are 

 intentionallj' the means for simplifying instruction, 

 will always be valuable, even if we have the 

 original preparations under the microscope before 

 us. We must consider the relative merits of 

 photographs and of drawings which purport to be 

 exact representations of what is seen under the 

 microscope. Thus in the case of micro-organisms, 

 when their biological characters are studied under 

 low powers of the microscojae, photograjjhs are 

 preferable because they give a more faithful re- 

 presentation. At the same time, apart from this 

 comparative value, we must not lose sight of the 

 actual value of photograph}' in placing within the 

 reach of the student or investigator, who may not 

 be a draughtsman, a most valuable means for 

 illusti'ating all kinds of preparations. 



For double-stained or triple-stained tissue pre- 

 parations an accurately coloured drawing leaves 

 little to be desired ; but if we reproduce the same 

 by a wood engraving, and so lose the advantage 

 of the coloured picture, which is instructive in 

 indicating the method of staining, a photograph will, in many cases, 

 be far more satisfactory. 



When we have to deal with the growth of bacteria en masse, 

 as in test-tube and plate-cultivations, with colonies as seen under 

 a low power of the microscope, and with impression-prepara- 

 tions both under low and high powers, unless the bacteriologist 

 is a most accompli-shed draughtsman as well as an accurate and 

 reliable observer, photography undoubtedly affords the best mode 

 of illustration. The apparatus being ready and at hand, a negative 

 can be produced in a few minute's of a preparation which, from the 

 amount of detail it contains, would take perhaps several hours to 

 draw and colour. From that negative any number of facsimiles can 



I'iG. 82. — Photo- 

 geaph of a 

 Cultivation op 

 Bacillus An- 

 thkaois. 



