THE PROBABLE ACTION OF LIPOIDS IN GROWTH. 



By D. T. MacDOUGAL. 



{Read April 21, 1922.) 



Accumulating evidence, including biochemical tests of the occur- 

 rence of lipoids in cells, especially abundant in the accretion stage of 

 growth, microscopic and ultra-microscopic examinations of plasma 

 and wall, the use of reagents which would displace or liquefy lipoids 

 in the modification of permeability, all support the conclusion that the 

 lipoids constitute the external layer of the plasma sending a pene- 

 trating meshwork into both the plasma and the wall. 



The implied view would make the lipoids the fundamental struc- 

 ture of protoplasm and the primary factor in all exchanges between 

 the cell and the medium. The facts cited cause renewed interest in 

 the original proposal of Quincke in 1888 and of Overton in 1895 and 

 1899 as to the lipoid theory of the plasmatic membrane. 



Additional information concerning the nature and action of some 

 of the common lipoids, and of the nature of hydration, together with 

 exact determinations of the influence of various ions on permeability, 

 gives opportunity for the consideration of the subject from new 

 angles. 



1. The experimental results which concern the matter and which 

 are described in the present paper have been obtained by two methods. 

 Measurements of endosmose in artificial cells, with a plasmatic lining 

 including lipoids, have been made. These results have been corre- 

 lated with measurements of the hydration reactions of biocolloids, 

 and living and dried cell-masses in the solutions used in the osmotic 

 tests. 



2. Lecithin incorporated in the plasmatic jelly layer of an artificial' 

 cell has but little effect on the osmotic action. The same substance 

 deposited as a layer between the plasmatic jelly and the outer wall 

 lessens the permeability of the system and increases the osmotic effect. 



PROC. AMER. PHIL. SOC, VOL. LXI., C, AUG. 12, I922. 



