igi2] E. Newton Harvey 5^ 



according to the degree of shaking. The role of the lecithin is to 

 hold the water as the water replaces the Chloroform. The protein 

 membrane is impermeable to lecithin. 



These artificial lecithin cells are stable, persisting until destroyed 

 by bacteria. In many ways — in shape, in general appearance and in 

 consistency — they resemble, to a very remarkable degree, sea-tirchin 

 or star-fish eggs. Some of their properties have been described in 

 Science (n. s.), V'ol. 36, p. 564, 1912. 



The point I wish to emphasize here, however, is not that we 

 can prepare artificial cells closely resembling real cells, but that a 

 Solution of lecithin may be obtained within a protein membrane, 

 the whole of known composition and of a size comparable with cell 

 sizes. Much can be inferred concerning the living cell from a 

 knowledge of the properties of such artificial cells where compo- 

 sition is definitely known. 



As Chloroform is exchanged for water, some of the lecithin 

 separates in the form of granules, most of which agglutinate in a 

 dense clump. The cell as a whole, but more particularly these 

 granules, take up neutral red from dilute Solution, becoming red 

 in color. (Chloroform alone takes up only the yellow base of neu- 

 tral red. When lecithin is dissolved in Chloroform it unites with 

 the yellow base, forming a red salt.) 



If the permeability for alkalies of such red-stained cells is 

 studied, a marked difference from that of living cells is noted. 

 Both ammonium hydroxid and sodium hydroxid in w/2000 con- 

 centration enter rapidly and at the same rate. It will be remem- 

 bered that all living cells are very easily permeable to ammonium 

 hydroxid, but very slightly so to sodium hydroxid.^ The surface 

 membrane of living cells is evidently of quite different composition 

 from the protein film which condenses on Chloroform droplets. 



Living cells behave toward alkalies as though they were sur- 

 rounded by a layer of a fat solvent, as postulated by Overton. 

 Lipoid-soluble alkalies (ammonium hydroxid) penetrate readily, 

 lipoid-insoluble alkalies (sodium hydroxid) do not. The lipoid 

 solubility of ammonium hydroxid can be readily demonstrated by 

 means of a benzol-lecithin Solution shaken with egg albumen solu- 



^ Harvey, E. N. : Journal of Experiniental Zoology, 10, p. 507, 1911 and 

 BiocHEMicAL Bulletin, i, p. 227, 1911. 



