302 TECHNICAL MICROSCOPY. 



would be wholly inaccurate. This is also true of other stratified 

 membranes (III., 18, 26-28), as well as in the illustration of starch- 

 grains. As regards cell-masses, sometimes the double-outlined mem- 

 branes are figured as light, while those of the surrounding cells are 

 shaded, and so on ; indeed, all the microscopic figures of Schacht 

 that we have seen are represented diagrammatically. It is almost 

 superfluous to remark that we by no means wish to disparage them 

 on this account, for diagrammatic representation has just as much 

 claim to general approval as any other method. We merely wish 

 to establish a fact which appears to be but little known. 



The individual discretion which the observer may use in the 

 combination of different focal adjustments must be added to 

 the arbitrariness which he usually permits himself to exercise in 

 delineating microscopic objects. Sections through parenchymatous 

 tissues, for instance, are not seldom represented as though the 

 single cells were situated exactly at the same height, and had 

 been cut right through the middle. In spiral vessels, annular 

 vessels, &c., the surface view is frequently combined with the 

 central sectional view; occasionally, too, we find the opposite 

 sides combined together in one view. Other draughtsmen 

 are accustomed mentally to enlarge microscopic objects to 

 any extent, and then to draw them as they would appear 

 to the naked eye, with reflected or transmitted light. 

 Fig. 169, for instance, is a spiral thread, depicted upon this 

 principle. The greatest freedom is here taken by the 

 draughtsman, for he supposes cell-membranes, which are 

 at the same time transparent and opaque, transparent, 

 inasmuch as the projecting concretions (annular and spiral 

 FIG. 169. threads, &c.) are figured as if visible ; opaque with regard 

 to the course of the spiral and the shading of the sur- 

 rounding sheath (at the points where they cross only the front side 

 is drawn). The spiral itself is shaded partly on the one side and 

 partly on the other, though no really definite effect of illumination 

 is assumed in either case. Briefly, in the delineation of micro- 

 scopic objects, disregarding their mere form, which each reproduces 

 according to his ability, there exists a degree of arbitrariness which 

 no words can express. 



The contradictions affecting the usual methods of representing 

 objects are by no means easily explained. On the one hand, plane 

 .microscopic vision with transmitted light and large aperture of 



