VI] MACALLUM'S EXPERIMENTS 289 



By this means Macalluni demonstrated some years ago the 

 unexpected presence of accumulations of potassium (i.e. of chloride 

 or other salts of potassium) localised in particular parts of various 

 cells, both solitary cells and tissue cells ; and he arrived at the 

 conclusion that the localised accumulations in question were 

 simply evidences of concentration of the dissolved potassium salts, 

 formed and localised in accordance with the Gibbs-Thomson law. 

 In other words, these accumulations, occurring as they actually do 

 in connection with various boundary surfaces, are evidence, when 

 they appear irregularly distributed over such a surface, of in- 

 equalities in its surface tension* ; and we may safely take it that 

 our potassium salts, like inorganic substances in general, tend to 

 raise the surface tension, and will therefore be found concentrating 

 at a portion of the surface whose tension is weakf. 



In Professor Macallum's figure (Fig. 98, 1) of the little green 

 alga Pleurocarpus, we see that one side of the cell is beginning to 

 bulge out ill a wide convexity. This bulge is, in the first place, 

 a sign of weakened surface tension on one side of the cell, which as 

 a whole had hitherto been a symmetrical cyhnder ; in the second 

 place, we see that the bulging area corresponds to the position of 

 a great concentration of the potassic salt ; while in the third place, 

 from the physiological point of view, we call the phenomenon 

 the first stage in the process of conjugation. In Fig. 98, 2, of 

 Mesocarpus (a close ally of Spirogyra), we see the same phenomenon 

 admirably exemplified in a later stage. From the adjacent cells 

 distinct outgrowths are being emitted, where the surface tension has 

 been weakened : just as the glass-blower warms and softens a small 

 part of his tube to blow out the softened area into a bubble or 

 diverticulum ; and in our Mesocarpus cells (besides a certain 

 amount of potassium rendered visible over the boundary which 



between such experiments as these of Professor Macallum's and the ordinary 

 staining processes of the histologist. The latter are (as a general rule) purely- 

 empirical, while the former endeavour to reveal the true microchemistry of the 

 cell. "On pent dire que la microchimie n'est encore qu'a la periode d'essai, et 

 que I'avenir de I'histologie et specialement de la cytologie est tout entier dans la 

 microchimie" (Prenant, A., Methodes et resultats de la Microchimie, Jourti. de 

 VAnat. et de la Physiol, xlvi, pp. 343-404, 1910). 



* Cf. Macallum, Presidential Address, Section I, Brit. Ass. Rep. (Sheffield), 

 1910, p. 744. 



t In accordance with a simple corollary to the Gibbs-Thomson law. 



T. G. 19 



