R. R. Bensley qq 



32-38 per cent of the dried product, with a great many preparations yielding 

 about 34 per cent. The phospholipid content of this fat, computed as lecithin 

 from phosphorus determinations, is from 45-58 per cent by weight of the 

 whole fat, and corresponds well with the ratio lecithin x 100 ^^^ ^^^ whole 

 liver. f^t 



The submicroscopic particles other than glycogen have a higher fat content, 

 ranging from 42-51 per cent of dry weight with about the same or slightly 

 higher percentage of phospholipid. Both particles also contain sterols, and, as 

 pointed out by Claude, the extracted lecithin dissolved in glacial acetic acid 

 gives a positive reaction with Schiff's reagent for aldehydes, indicating a con- 

 tent of acetal-phosphatide. 



The fat content of the liver in different nutritional states varies within wide 

 limits, but rarely rises above 20 per cent of the dry weight. Mitochondria and 

 submicroscopic particulates therefore contain a much higher percentage of 

 their dry weight in the form of fat than the whole liver. This indicates that 

 some other portion of the cell contains less. 



It may be recalled at this point that in a series of splendid and significant 

 researches Bungenberg de Jong'^ has explored the conditions of precipitation 

 in lecithin emulsions and in mixtures with known content of lecithin, protein, 

 fat, fatty acids, and various electrolytes. The precipitations observed under 

 these conditions he termed "coacervates." These observations and experi- 

 ments have received little consideration from cytologists, who did not per- 

 ceive that they had a bearing on the structure of protoplasm. Others brushed 

 them aside with the statement that it was just a new name for flocculation, 

 without perceiving that for the first time a quantitative study of flocculation 

 had been made which gave us an insight into the complex composition of 

 particles visible in cells or separable from them. Bungenberg de Jong's 

 speculations are fully confirmed by the discovery of the true composition of 

 mitochondria and of the cytoplasmic submicroscopic particulates of Claude. 



The experiments of Bungenberg de Jong definitely raise the question as 

 to whether lecithin and fats can exist as molecularly dispersed substances in 

 cytoplasm, a question already answered tentatively in the negative for lecithin 

 by McLean and McLean^" and by Bloor." This problem can now be solved 

 by the use of the methods of investigation introduced by Bensley and Hoerr 

 and extended by Claude. In some types of cell, as for example the liver, the 

 various particulates can be removed seriatijn, examined chemically, and the 

 residual suspension in turn explored for its contents of proteins and lipids. 



In a long series of investigations directed principally to the problem of 

 the composition of the particulates in the liver cell of the guinea pig my as- 

 sistant Dr. Lazarow and I have been impressed with the fact that, as the 

 particulates are removed by mechanical means, both the protein content and 

 the lipid content of the supernatant solution are reduced, but that the lipid 

 diminishes at a more rapid rate than the protein. A series of experiments 



