210 PROTOPLASM 



appearance of a network depend, which may be of such con- 

 sequence for our studies on protoplasm ? It is certain that 

 the granules are often actually directly connected to one 

 another : one can convince oneself of this fact by rubbing up 

 a small quantity of ink with glycerine jelly and mounting it, 

 and also by moistening a little of the soot on a slightly 

 blackened cover glass with oil and investigating it. Granules 

 can then frequently be seen to be connected together, and 

 apparently united by a dark, short filament, giving rise to a 

 dumb-bell shaped structure. I regard, however, the latter 

 phenomenon as to a great extent an optical one, the 

 explanation of which will not be further attempted here. 

 If one examines fine drops of oil, such as can be easily 

 produced by shaking up olive oil with weak soda solution, 

 one notices also that two drops in close contact when 

 sharply focussed seem to pass into one another directly by 

 means of a dark bridge at their point of contact. It is self- 

 evident that in this case a real connection does not exist, 

 since otherwise they would necessarily flow together. 

 We must, I think, put a similar value upon the above- 

 mentioned dumb-bell shaped figures of the adherent ink 

 granules. The network described, however, can only in part 

 depend upon this connection of the ink granules. In the 

 main it may depend upon another optical phenomenon. 



If single isolated quiescent ink granules be studied in 

 glycerine jelly or oil, it may be seen that each granule, when 

 focussed as sharply as possible, so that it appears dark and 

 sharply contoured, is surrounded by a clear area, which has 

 a breadth of about the diameter of the granule, or rather 

 more, and is marked off from the rest of the field of vision 

 by a rather darker, dull border. This is the so-called 

 diffraction area, which is seen in the microscopic image 

 round all bodies of greater or less refracting power, and 

 which by Nageli and Schwendener (1877, pp. 230-236) was 

 referred partly to the direct reflection of the incident light 

 at the edge of the body in question, partly to the interference 

 of this reflected light with the light which comes through 

 unreflected. If one slightly raises or lowers the tube of the 

 microscope, the granule disappears, but in both cases the 



