PREPARATION AND DETERMINATION OF LECITHIN 
203 
ether, and hence for any organized tissue the latter solvent has a poor penetrating 
power, and long continued and repeated extraction is necessary in order to make 
certain of complete extraction of any lecithin which may be free in the tissue. 
Secondly, it has been shown that lecithin, in part at least, exists in combination 
with albumin forming the so-called lecith-albumins, and it has been shown that the 
lecithin in these is not dissolved out by ether even on repeated extraction. 
Thirdly, no separation occurs in the extraction with ether, because all the bodies 
concerned, viz., fats, cholestearin, and lecithin, are all easily soluble in ether, and hence 
the ethereal extract is loaded up with fats and cholestearin which are present in such 
large comparative quantity that it becomes afterwards exceedingly difficult to purify. 
Alcohol possesses the advantage over ether as a first extracting agent, in that it 
takes up the water ot the tissue and penetrates to all parts, it also coagulates the 
proteid, and hence breaks up the lecith-albumins and allows the whole of the lecithin 
to be extracted. 
A consideration of the solubilities of the fats, cholestearin, and lecithin in alcohol 
at different temperatures indicates that a considerable amount of separation of the 
lecithin from the fats and cholestearin may be effected, in the first instance, by using 
the alcohol at ordinary atmospheric temperatures (io-20°C), instead of as has 
usually been done, employing the alcohol at a temperature of 40-50 0 C. 
All the bodies concerned are readily soluble in alcohol at the higher temperatures, 
but at room temperatures the oils and cholestearin are only sparingly soluble, while 
lecithin still possesses a high solubility, and does not begin to pass out of solution in 
large amounts until the temperature falls below o° C. 
Thus, when a fat or oil is treated with alcohol at room temperature only a 
small amount dissolves, but on heating the fat passes into solution readily, and on 
cooling the excess is again thrown out. Cholestearin also does not dissolve appre- 
ciably in alcohol at 10-15 0 C, but on heating dissolves readily, and crystallizes out 
again in great part on cooling. Lecithin, on the other hand, dissolves quite readily 
in alcohol at room temperatures. 
We have used this in conjunction with acetone precipitation as a method of 
separating and estimating lecithin, and have found it to yield good results. 
The method in outline may be described as follows : — The material to be tested 
(egg yolk was used in our experiments) is weighed and extracted with three to four 
- times its weight of cold alcohol (methylated spirit of ninety-five per cent, or absolute 
alcohol), each quantity of alcohol being left for two or three hours in contact with 
the material. Each time filtration through linen is used for separating the alcoholic 
extract, and at the end the three clear extracts are united and the alcohol evaporated 
off preferably in vacuo until a syrup is obtained. The syrup is taken up in a small 
volume of ether and precipitated with excess of acetone added as long as a precipitate 
is obtained. The lecithin is completely thrown out of solution, as is shown by a 
