482 THE FORMS OF TISSUES [ch. 



impinges upon it; and, suuject to this limitation, the rule is strictly 

 true. 



While thes^ writers regarded the form and arrangement of the 

 cell-wdls as a biological phenomenon, with little if any direct 

 relation to ordinary physical laws, or wioh but a vague reference 

 to "mechanical conditions," the physical side of the case was 

 soon urged by others, with more or less force and cogency. Indeed 

 the general resemblance between a cellular tissue and a "froth" 

 had been pointed out long before. Robert Hooke described the 

 cells within the shaft of a feather as forming "a kind of solid or 

 hardened froth, or a congeries of very small bubbles," and Grew 

 described a parenchyma as made by "fermentation", "as we see 

 Bread in Baking", and again as being "much the same thing, as to 

 its construction which the froth of beer or eggs is." Later on, within 

 the days of the cell-theory, Melsens made an "artificial tissue" by 

 blowing into a solution of white of egg*. 



In 1886, Berthold pubhshed his Protoplasmamechanik, in which he 

 definitely adopted the principle of "minimal areas," and, following 

 on the lines of Plateau, compared the forms of many cells and the 

 arrangement of their partitions with those assumed under surface- 

 tension by a system of "weightless films." But, as Klebs| pointed 

 out, in reviewing the book, Berthold was so cautious as to stop short 

 of attributing the biological phenomena to a mechanical cause. 

 They remained for him, as they had done for Sachs, so many 

 "phenomena of growth," or "properties of protoplasm." 



In the same year, but while still unacquainted, apparently, with 

 Berthold's work, Leo Errera pubhshed a short but very striking 

 article J in which he definitely ascribed to the cell-wall (as 

 Hofmeister had already done) the properties of a semi-liquid film, 

 and drew from this as a logical consequence the deduction that it 

 must assume the various configurations which the law of minimal 

 areas imposes on the soap-bubble. So what we may call Errera's 

 Law is formulated as follows: A cell- wall, at the moment of its 



* C.R. xxxin, p. 247, 1851; Ann. de chimie et de phys. (3), xxxra, p. 170, 1851 ; 

 Bull. R. Acad. Belg. xxiv, p. 531, 1857. 



t Georg Klebs, Biol. Centralbl. vn, pp. 193-201, 1887. 



X L. Errera, Sur une condition fondaraentale d'equilibre des cellules vivantes, 

 C.R. cm, p. 822, 1886; Bull. Soc. Beige de Microscopie, xm, Oct. 1886: Recueil 

 d'ceuvres {Physiologie gdnirale), 1910, pp. 201-205. 



