CRITICISM OF FROMMANN 83 



the vacuoles interrupted only here and there by gaps ; but if 

 the drops are spread out flat on a slide, the walls of the 

 vacuoles become torn in many places and are drawn out, so 

 that at intervals in the place of vacuoles there arises only 

 a framework of oil interrupted in many places by gaps, 

 some smaller, some larger." I will not enter here into the 

 obvious supposition as to what occasioned the origin of this 

 framework of oil, when the drop of linseed oil, with droplets 

 of water in its interior, was spread out on the slide. It is 

 sufficient for me to have shown by the above-made quotation 

 that Frommann actually puts forward the view, that between 

 neighbouring drops of water suspended in fluid linseed oil 

 gaps may exist in the fluid oil lamellae separating them, 

 without the partially continuous drops of water flowing to- 

 gether, and that similarly he entertains the opinion, that 

 a net-like framework consisting of fluid oil can remain 

 suspended in water. Since both these things are physically 

 impossible, Frommann must have seen gaps where none were 

 present. But this .fact makes us also very doubtful as to 

 his observations on the viscid froths, the more so as he gives 

 us no information as to the optical means by which his 

 investigations were carried on. We know, however, that an 

 accurate investigation of the froths requires the strongest 

 systems and oculars. Hence it appears to me that From- 

 mann has not recognised the finest portions of the froths at 

 all ; at least he speaks of the fact that between the vacuoles 

 of the froth-drops " a fine and faintly granulated substance 

 occurs everywhere, which very probably consists of oil in 

 a state of the finest emulsive division" (p. 665), or notices 

 on p. 667 "a pale, finely granular, or indistinctly granulo- 

 fibrillar material between the vacuoles." So far as I am 

 acquainted with the froths, this material can only have been 

 foam of the minutest structure, from which fact it is a 

 legitimate conclusion, that the investigations were carried 

 on with insufficient magnification. 



I may take this occasion, however, to remark, that in 

 very thinly spread out marginal portions of foam, which 

 stick to the slide or the cover-slip, or even in very small 

 drops of foam, where it is often possible to see larger foam 



