CHEMISTRY OF THE CELL NUCLEUS 211 



physical chemistry, which it may be interesting to briefly 

 allude to, and so bring this article to a conclusion. 



In 1876 Butschli suggested that cell division is brought 

 about by an increase of surface tension subsequent to nuclear 

 division in the equatorial region of the egg-cell. But, as 

 Brailsford Robertson has recently pointed out in an article 

 on the "Chemical Mechanics of Cell Division," 1 this would 

 result in a streaming of material towards the equator and not 

 away from it, which is what really takes place. He adduces 

 evidence to show that surface-tension is lowered at the equator, 

 and not raised as Butschli supposed. 



In our account so far of the chemistry of the nucleus, we 

 have considered mainly the proteins and protein-like substances, 

 because it is in connection with these that our knowledge is 

 greatest. It must not, however, be forgotten that there is in all 

 cells, and doubtless in their nuclei too, another important group 

 of substances of a labile nature which participate in the metabolic 

 cycle. The group is a heterogeneous one from the chemical 

 standpoint, and Overton's term lipoid is now very generally 

 applied to it. The lipoids are so called on account of their 

 solubilities being like those of fats, and they include substances 

 free from both nitrogen and phosphorus {e.g. cholesterin), 

 nitrogenous galactosides free from phosphorus, and certain 

 highly complex nitrogenous and phosphorised fats which 

 were originally termed phosphatides by Thudichum. Lecithin 

 is the best known example of these, and yields on decomposition 

 phosphoric acid, fatty acid, and a nitrogenous base known as 

 choline. 



Brailsford Robertson has shown that if a thread moistened 

 with a base is laid across a drop of oil containing a trace of 

 fatty acid, the drop undergoes division along the diameter on 

 which the thread lies. If the thread is moistened with soap, the 

 same result follows ; and therefore the explanation advanced for 

 the division of the drop in the first experiment is that soap 

 formation occurs— that is, the base on the thread and the fatty 

 acid in the oil combine together. The soap lowers the surface 

 tension in the equator of the drop, and this brings about the 

 streaming movements away from the equator which culminate 

 in the division of the drop into two ; and he finally suggests 



1 Issued as a Bulletin from J. Loeb's Laboratory (University of California 

 publications, 1909). 



