340 RETROGRESSIVE PROCESSES 



with marked and complete disintegration of both nucleus and 

 cytoplasm. Furthermore, we have yet to explain why, under 

 some conditions, the fat is removed from the fat depots to be 

 stored up in the liver or other organs. By applying the facts 

 recently brought out concerning fat metabolism, particularly by 

 Kastle and Loevenhart, 1 a satisfactory explanation seems to be 

 possible. Fat is always utilized and transported in the form 

 of its two constituents, fatty acid (or soaps) and glycerin, which 

 are diffusible and soluble. It enters and leaves the cells in this 

 condition, being split or combined, as may be necessary to pro- 

 duce equilibrium, by the action of lipase, which is present 

 within the cells and in the blood and lymph. Under normal 

 conditions there is little free visible fat in the cells of the paren- 

 chymatous organs, because it is largely used up through oxida- 

 tion of the glycerin and fatty acids by the action of the intra- 

 cellular oxidases. Where there is abundant lipase and but 

 little oxidative activity, as is the case in the areolar fat tissue, 

 fat accumulates in large amounts. When, for any reason, the 

 oxidative power of the parenchymatous organs is reduced, fat 

 accumulates in them as it does in the fat depots normally, and 

 we have an excess of fat in the parenchymatous cells ; thus, in 

 pulmonary tuberculosis, severe or protracted anemias, etc., a 

 great accumulation of fat occurs, particularly in the liver, where 

 normally active oxidative processes continually balance the 

 action of the abundant lipase of the liver-cells. 



If the fat accumulates in cells that are structurally normal or 

 nearly so, the fat-droplets fuse together under the pressure of 

 the cytoplasm, and we get tne picture of a typical fatty in- 

 filtration. If the cells are much disintegrated through the 

 action of the poison, e. g., phosphorus, bacterial toxins, etc., 

 the accumulating fat-droplets are not crowded into one large 

 droplet, but lie free in the granular debris of the disintegrating 

 cell, constituting the typical appearance of fatty degeneration. 

 Fatty degeneration is usually brought about by poisons, while 

 fatty infiltration depends usually upon decreased oxidation, due 

 to lack of either oxygen or hemoglobin in the blood. If the 

 anemia is extreme, however, the cells degenerate, and then we 

 find a true fatty degeneration caused by lack of oxygen. Thus, 

 in an anemic infarct fat accumulates about the periphery of the 

 dead area, 2 probably because fatty acids and glycerin diffuse in 

 slowly from the surrounding parts where circulation still goes 

 on, and are built up into fat by the cell lipase, for in anemic 



1 See consideration of this topic on page 67, 



2 Fischler, Cent. f. Path., 1902 (13), 417. 



