102 



Cytoplasmic Localization o£ Lipids 



centrifugation is directly comparable to the results obtained in the liver. The 

 percentage loss of other fats is less than in the case of the liver and the ratio 

 of residual fat to residual protein is higher. 



The difference in the completeness of the removal in the different experi- 

 ments is probably due in part to small globules of fat surrounded by protein 

 haptene membranes failing to precipitate or to rise in the process of centrifuga- 

 tion, and to carry-over of part of the precipitate in pouring off the supernatant 

 because of loose packing in the centrifuge tube. 



In spite of the completeness of removal of dispersed fats and phospholipids 

 in these experiments, I do not wish to convey the impression that all these 

 substances are contained in mitochondria and submicroscopic particulates. 



The neutral fats, sterols, and sterol esters occur also as discrete globules which, 

 however, contain no phospholipid. The structural proteins of the cell remain- 

 ing undissolved after successive extraction of the cell with normal saline, 

 10 per cent saline, and 0.005N ammonia in distilled water still contain ap- 

 proximately 25 per cent of their dry weight in the form of lipids. 



The active participation of lipids must be suspected in the formation of 

 intracellular droplets of a transient sort such as secretion granules, in particu- 

 lar those which brown with osmic acid, such as the zymogen granules of the 

 stomach and pancreas, and artificial droplets such as the neutral red granules 

 of Parat. Nencki and Sieber^" found 10 per cent of lecithin in the crude pepsin 

 obtained by dialysis against distilled water from clear gastric juice obtained 

 by sham feeding from a gastric fistula. 



Summary 



It has been found that nearly all of the invisible lipids of the cytoplasm of 



the hepatic cell of the guinea pig are contained in the particulate components 



of the protoplasm and in other structural elements, and that the interparticu- 



late cell water, while containing much protein, contains a negligible quantity 



of lipids. 



REFERENCES 



1. Grafflin, A. L.: Anat. Recrd. 77:473, 1940. 



2. Marble, H.; Grafflin, A. L., and Smith, R. M.: Jl. Biol. Chem. 134:253, 1940. 



3. Rosenfeld, G.: Ergbne. d. Physiol., I. Abtl. (Biochem.) 2:50, 1903. 



4. Leathes, J. B., and Raper, H. S.: The Fats (2d ed.; London: 1925). 



5. Gorter, E., and Grendel, F.: Jl. ExjDcr. Med. 41:439, 1925. 



