ON TflE STAfE OF SOLUTION OF PROTEIDS. 429 



ftrtificially sdiiie sort of proteid membrane associated with Ijodies lielong- 

 ing to the lipoid class which would imitate, as far as possible, in its 

 properties the pellicle on the surface of the mammalian blood corpuscle. 



The preparation of the lipoid substances in quantity and in a fair 

 state of purity has naturally occupied much time. The lecithin, kephalin, 

 and cerebrin were separated from sheep's brains, the method of Waldemar 

 Koch being to a large extent followed. 



After boiling out thoroughly with acetone for many hours, to remove 

 water and extractives, the acetone was driven off by heat and the residue 

 repeatedly extracted with large volumes of pure ether. 



This extract, holding the lecithin and kephalin, was allowed to 

 evaporate during a month slowly to about a quarter of its original 

 volume. 



Meanwhile the ether-extracted brain matter was boiled out many 

 times with alcohol and the crude cerebrin separated by cooling to 0° C. 

 This product was then repeatedly crystallised from hot glacial acetic acid 

 and dried in vacuo over lime. The resulting substance had a melting- 

 point of 188° C, taken in a bath of sulphuric acid. 



From the ethereal extract holding the kephalin and lecithin the 

 former was separated by adding excess of absolute alcohol and the filtrate 

 set aside for subsequent removal of lecithin. 



The crude kephalin was extracted many times with boiling alcohol 

 dissolved in ether and precipitated with acetone. 



It was finally again dissolved in ether, allowed to stand, the ether 

 evaporated, crystallisation twice carried out from hot acetic ether, and 

 dried in vacuo over sulphuric acid. 



The crude lecithin was recovered from the solution in alcohol and 

 ether above mentioned by evaporation of the solvents, again dissolved in 

 pure ether, and freed of cholesterine by precipitation of the solution 

 ■with acetone. The precipitated lecithin was then taken up in cold 

 alcohol, filtered, evaporated, and finally three times crystallised from 

 hot acetic ether and dried in vacuo over sulphuric acid. 



The oleic-acid ester of cholesterine was also prepared by heating pure 

 cholesterine and oleic acid together at 200° C. for several hours and 

 repeatedly crystallising the product from hot alcohol till a melting-point 

 of 42° C. was reached. 



With the material so prepared a series of experiments is in hand 

 in which various membranes have been constructed and tested for per- 

 meability to salts. The following membranes are some of those so far 

 put to the test : — 



(a) Lecithin emulsion (obtained by pouring ethereal solution into 

 water) and 10 per cent, gelatine supported in the pores of peritoneal 

 membrane. 



(b) Peritoneal membranes soaked in blood serum and treated with 

 ethereal solution of lecithin. 



(c) The same as (b), but using white of egg in place of blood serum. 



(d) Celloidin lecithin membranes. 



(e) Peritoneal membi-ane with cholesteryl oleate in the pofes. 

 (/) Same as (e), but using kephalin. 



It has been found that over long periods none of these membranes are 

 impermeable to either sodic or potassic chloride, but the rate of initial 

 osmosis is by no mep.ns the same in the different cases, 



