132 Scientific Proceedings (44). 
Percentage of Total Nitrogen. 
Periods. 
Urea N, 
per cent. 
Ammonia 
N, per 
cent. 
Creatin and 
Creatinin N, 
per cent. 
Purin N, 
per cent. 
Undeter- 
mined N, 
per cent. 
88.5 
3.64 
2.51 
0.l6 
5.19 
II. (First injection period) 
85.7 
3-75 
2.50 
0.20 
7.86 
III. (First post injection 
86.5 
3.6l 
3-33 
O.24 
6.32 
86.7 
3-65 
3-20 
0.19 
6.26 
V. (Second in j ection period ) 
87.0 
3.92 
3-73 
0.l6 
5.19 
VI. (Second post injection 
84.2 
4.29 
3.62 
0.17 
7.72 
81 (606) 
Experiments on the diffusibility of cholesterol-esters 
and of lecithan compounds. 1 
By ERNST BOAS and JACOB ROSENBLOOM. 
[From the Laboratory of Biological Chemistry of Columbia University, 
at the College of Physicians and Surgeons, New York.] 
I. Cholesterol Esters. 
It has been shown in this laboratory that ether solutions of 
various biological substances pass through rubber membranes into 
ether. 
We have found that cholesterol-benzoate, cholesterol-stearate, 
cholesterol-oleate and cholesterol-palmitate dissolved in ether will 
readily diffuse through rubber into ether. 
Cholesterol-stearate with a molecular weight of 652.61 diffuses, 
whereas the various lecithans, with molecular weights considered 
to be 770 to 785, do not. If we assume that the diffusion of a 
substance depends on the size of its molecules, the above facts 
strengthen Hiestand's conclusion that the molecular weight of 
egg-yolk lecithin is 1446, which figure he obtained by a molecular 
weight determination. 
J This study is one of a projected series on lipins, which in turn constitutes a 
section of a comprehensive plan of research on the composition of protoplasm as 
well as the structural and dynamic relationships of cell constituents and products. 
These investigations are now in progress in the Laboratory of Biological Chemistry 
of Columbia University, at the College of Physicians and Surgeons, and under the 
auspices of the George Crocker Special Research Fund. 
