306 THE FORMS OF TISSUES [ch. 



had been pointed out long before, by Melsens, who had made an 

 "artificial tissue" by blowing into a solution of white of egg*. 



In 1886, Berthold pubUshed his Protoplasmamechanik, in which 

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

 following on the lines of Plateau, compared the forms of many 

 cell-surfaces and the arrangement of their partitions with those 

 assumed under surface tension by a system of " weightless films." 

 But, as Klebs| points out in reviewing Berthold's book, Berthold 

 was careful to stop short of attributing the biological phenomena 

 to a definite 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 apparently unacquainted with 

 Berthold's work, ErreraJ published a short but very lucid article, 

 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 Errerd's Law is formulated 

 as follows : A cellular membrane, at the moment of its formation, 

 tends to assume the form which would be assumed, under the 

 same conditions, by a liquid film destitute of weight. 



Soon afterwards Chabry. in discussing the embryology of the 

 Ascidians, indicated many of the points in which the contacts 

 between cells repeat the surface-tension phenomena of the soap- 

 bubble, and came to the conclusion that part, at least, of the 

 embryological phenomena were purely physical §; and the same 

 line of investigation and thought were pursued and developed by 

 Robert, in connection with the embryology of the Mollusca||. 

 Driesch again, in a series of papers, continued to draw attention 

 to the presence of capillary phenomena in the segmenting cells 



* C. R. Acad. 8c. xxxiii, p. 247, 1851; Ann. de chimie et de phys. (3), xxxm, 

 p. 170, 1851; Bull. R. Acad. Belg. xxiv, p. 531, 1857. 



t Klebs, Biolog. Centralbl. vn, pp. 193-201, 1^87. 



{ L. Errera, Sur une condition fondamentale d'equUibre des cellules vivantes, 

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

 fTcBUvres (Physiologie generale), 1910, pp. 201-205. 



§ L. Chabry, Embryologie des Ascidiens, J. Anat. et Physiol, xxm, p. 266, 1887. 



II Robert, Embryologie des Troques, Arch, de Zool. exp. et gen. (3), X, 1892. 



