404 RETROGRESSIVE CHANGES 



contained in a degenerated kidney. A pathologic kidney containing 

 16 per cent, of lipins ( 18 per cent, is about the average amount in normal 

 human kidneys) may show extreme "fatty degeneration" under the 

 microscope, whereas another kidney may contain as much as 23 per 

 cent, of hpins, yet not show any fat whatever by staining methods. 

 The explanation of this remarkable discrepancy is as follows: 

 Every tissue and organ seems to contain a greater or less amount of 

 lipins, varying from 5 per cent, to 20 per cent, of the total dry weight 

 of the organ in the case of most of the important tissues, yet this is 

 usually held in such a form that it cannot be stained by any stains 

 available for the purpose. Thus in the kidneys, as before remarked, 

 we may have as much as 23 per cent, of lipins present and yet be unable 

 to stain any of it by ordinary methods. The greater part of this seems 

 to be essential to the cell, for it cannot be removed by the most extreme 

 starvation; e. g., the liver of the most emaciated dogs may contain 

 10 per cent, to 20 per cent, of fatty substances. Furthermore, the 

 same resistance is shown by part of the fat to extraction with ether. 

 A certain proportion of the fat can be extracted readily in twenty- 

 four hours or less by ether, but after this time no more can be made 

 to leave the tissues. Apparently the rest of the fat is held in a com- 

 bination that is insoluble in ether, and a large proportion of this fixed 

 material is not simple fat, but lecithin, cholesterol, and compounds of 

 these lipoids. It has also been demonstrated that fatty acids can 

 combine with amino-acids to form compounds (lipo-peptids) very 

 similar in their properties to these "masked" fats.^^ By digesting 

 the tissue for a short time by pepsin, however, the fixed lipins become 

 freed, so that they can then be readily dissolved out in ether. We see, 

 therefore, that much of the fat of normal cells is so firml}- combined 

 that it cannot be dissolved in ether, and under normal conditions all, 

 or nearly all, of it cannot be stained. (This applies particularly to 

 the parenchymatous organs; the fat of the areolar tissue is all readily 

 extracted — Taylor.) By the use of Ciaccio's method for microscopic 

 demonstration of intracellular lipoids, BelP'' has been able to demon- 

 strate in those cells that are fat-free by ordinary methods sufficient 

 lipoidal material to account for the normal "invisible fat," which is 

 probably identical with the "liposomes." But when pathological 

 changes in the cells result in decomposition of the cell protein through 

 autolysis, or produce physical changes in the colloids that hold the 

 lipins emulsionized, part of this normally invisible fat is set free, and, 

 becoming visible, "phanerosis," ^'^ produces the so-called "fatty degen- 

 eration." This explains the observations of Rosenfeld, cited above, 

 that kidneys may show much fat to the naked eye and microscopically, 

 when they actually contain even less than normal amounts of fat. Tay- 



12 Bondi, Biochem. Zcit., 1909 (17), 543. 



"Internat. Monats. Anat. u. Physiol., 1911 (28), 297; Jour. Med. Res., 1911 

 (24), 539. 



'* Klein perer, Deut. med. Woch., 1909 (35), 89. 



