FALSE NETWORK IN FOAMS 213 



network is lightened by the superposed diffraction rings of 

 three adjacent drops. In the case discussed, however, tin; 

 space between two adjacent droplets, which are a small 

 distance apart, is only illuminated by two diffraction rings, 

 and therefore appears a little darker an appearance which is 

 strengthened by contrast with the neighbouring clear meshes. 

 The origin of the thicker bridges can, for example, be very 

 distinctly observed, when a series of small drops is apposed 

 to the surface of a large one (Fig. 5, c, Plate X.). 



The observations which have just been described are a 

 warning to exercise the greatest caution in forming con- 

 clusions about reticular protoplasmic structures ; a great deal 

 of more detailed investigation is necessary in order to test 

 the earlier observations with a view to determining the 

 reality of the structures described. 



We have seen how reticular appearances of this kind 

 arise in strongly refracting droplets which are thickly 

 crowded together in a medium of less refracting power ; the 

 same thing can be shown, however, when we are dealing 

 with closely packed droplets of less refracting power in a 

 more strongly refractile medium, as in the earlier described 

 oil-froths, for example. If a very thin layer of such a froth 

 be investigated, not exceeding in thickness one layer of 

 alveoli, exactly the same phenomenon can be observed if one 

 places the focus a little above the exact median plane. With 

 a high focus the image of every less strongly refractile 

 droplet changes, as is well known, into that of a darker 

 point or granule. Round. each of these points, however, there 

 exists just such a diffraction ring as round the droplets of 

 stronger refraction, and these diffraction rings with their 

 borders then also produce just the same reticular appearance 

 with dark nodal points as has been described above. 

 Photograph II. reproduces this false reticular appearance 

 very beautifully, while Photograph I. shows the same spot at 

 a focus slightly below the median one. 



From these results it is certainly to be concluded that 

 in the microscopical observation of a thicker layer of such a 

 foam, there must be indications in many places of the 

 inwe of the false network mixed up with that of the real 



