752 TRANSACTIONS OF SECTION I. 



is manifest that in the formation of concentrated urines energy is expended. We 

 know also from the investigations of Barcroft and Brodie that the kidney during 

 diuresis absorbs much more oxygen per gram weight than the body generally, and 

 that, assuming it is used in the combustion of a proteid, a very large amount of 

 energy is set free, very much more indeed than is necessary- It has also been 

 observed that a portion of the energy set free is found in a higher temperature in 

 the excretion than obtains in the blood itself circulating through the kidney. This 

 large expenditure of energy is, probably, a result of the physiological adaptation 

 of the principle of the ' factor of safety,' which, as Meltzer has pointed out, 

 occurs in other organs of the body. 



In cell and nuclear division surface tension operates as a force, the action of 

 which cannot be completely understood till we know more of the part played by 

 the centrosomes and centrosphere. That this force takes part in cell reproduction 

 has already been suggested by Brailsford Robertson. lie has devised an ingenious 

 experiment to illustrate its action. If a thread moistened with a solution of a 

 base is laid across a drop of oil in which is dissolved some free fatty acid the drop 

 divides along the line of the thread. When the latter is moistened with soap 

 the drop divides in the same way and in the same plane. The soap formed in one 

 case and present in the other, it is explained, lowers the surface tension in the 

 equatorial plane of the drop, and this diminution results in streaming movement 

 away from that plane which bring about the division. He suggests that in cell 

 division there is a liberation of soaps in the plane of division which set up 

 streaming movements from that plane towards the poles and terminating in the 

 division of the cytoplasm of the cell. 



I have observed in the cells of Zygnema about to divide a remarkable condensa- 

 tion of potassium in the plane of division. In the 'resting' cell of this Alga the 

 potassium is, as a rule, more abundant in the cytoplasm near the transverse walls 

 of the thread, and only traces of the element are to be found along the line of 

 future division of the cell. But immediately after division has taken place the 

 potassium is concentrated in the plane of division. This would seem to indicate 

 that surface tension in the plane of division is, as postulated by the deduction from 

 the Gibbs-Thomson principle, lower than it is on the longitudinal surface, and 

 lower, especially, than it is on the previously formed transverse septa of the 

 thread. 



One must not, however, draw from this the conclusion that in all dividing 

 cells surface tension is lower in the plane of division than it is elsewhere on the 

 surface of the dividing structure. All that it means is that in the dividing cell 

 of Zygnema the condition already exists along the plane of division, which subse- 

 quently makes for low surface tension in the cell membrane immediately adjacent 

 to each transverse septum in the confervoid thread. If the evidence of low surface 

 tension vanished immediately after division was complete, then it might be held 

 that it determined the division. As it is, the low surface tension in this case is 

 the result and not the cause of the division. 



This conclusion is corroborated by the results of observations on the cells of tho 

 ovules of Lllium and Tvlvpa. The potassium salts in these are found condensed 

 in minute masses throughout the cytoplasm. When division is about to begin the 

 salts are shifted to the peripheral zone of the cytoplasm ; and when the nuclear 

 membrane disappears not a trace of potassium is now found in the neighbourhood 

 of the free chromosomes, a condition which continues till after nuclear division is 

 complete. The absence of potassium, the most abundant basic element in the 

 cytoplasm, would indicate that soaps are not present, and appropriate treatment 

 of such cells, hardened in formaline only, with Scarlet Red demonstrates that fats, 

 including lecithins, are absent also. This would seem to show that high instead 

 of low surface tension prevails about the nucleus during division. During the 

 'resting' condition of the nucleus this high tension is maintained, for, except in 

 very rare cases, and these of doubtful character, there is no condensation of 

 inorganic salts in the neighbourhood or on the surface of the nuclear membrane. 

 It is also to be noted that the nucleus, with exceptions, the majority of which 

 are found in the Protozoa, is of spherical shape, which also postulates that high 

 surface tension obtains either in the cytoplasmic layer about the nucleus or in the 

 nuclear membrane itself. It may also be suggested that high surface tension, 

 and not the physical impermeability of the nuclear membrane, is the reason why 

 the rjvtdev:s is, as I have often stated, wholly free from inorganic constituents. 



