CELLULAR TISSUE. 21 



tissue resembles the froth of a liquor in fermentation ; 

 Mirbel approves of this comparison thus far, that in 

 froth each bubble of air is separated from its neighbour 

 by a single film of water, and that the films are conti- 

 nuous one with another. Link approves of it also, 

 for this reason, that each bubble of air must be consi- 

 dered as surrounded by a watery membrane which is 

 peculiar to itself; and that, when they unite to form 

 the froth, each film of water is formed of two films ad- 

 hering together. Thus the partisans of the two 

 theories are divided even as to the meaning of simple 

 metaphors. 



Shall we venture to affirm any thing decisive between 

 these diametrically opposite opinions ? Is there any 

 intermediate theory which may reconcile them ? 1st. 

 Microscopic observation directed to this point has fre- 

 quently left me in doubt : the membrane which separates 

 the cellules appears simple with a microscope of small 

 power ; but as soon as we employ a powerful instrument 

 we very often can no more venture to affirm whether we 

 see a single or a double membrane ; and when it appears 

 double, whether this effect is due to some projecting 

 shadow. One thing I can affirm, and that is, that I 

 have seen triangular spaces between the cellules, as 

 are represented in the figures of Tre\nranus, Kieser, 

 and Amici ; and that wdth them I am inclined to con- 

 sider them as spaces filled with air : but one cannot 

 conclude from this that the tissue is not continuous 

 for it might easily happen that there might be among 

 the cellules full of juice some empty cellules, which 

 would present this appearance. Grew himself, always 

 admitting the simple nature of the membrane, has very 

 frequently represented intervals between the cellules, 

 very much the same as the authors whom I have pre- 

 viously quoted. 2d. In tearing irregularly the tissue 



