I'ATHOlJXilC.lL FAT ACri'Ml I.ATIOS 401 



sliowiiiy typiral Tatty degoueratiuu under the microscope was found 

 equal to or less than the normal amount — it was never increased. 

 The same conditions were found to obtain in human kidneys that 

 showed fatty nietaniorpliosis. .Microscoj)ic examination of s])ecimeiis 

 stained with tlie specific fat stains," therefore, uives no indication of 

 tlie amount of fat contained in a degenerated kidney. A pathok)<iic 

 kidney containing: 16 per cent, of lipins (18 per cent, is about the aver- 

 age amount in noi-mal human kidneys) inay sliow extreme "fatty de- 

 generation" under the microscoi)e, whereas anotlier kidney may con- 

 tain as mucli as 23 per cent, of lipins. yet not show any fat whatever 

 by staining methods. 



The explanation of tliis remarkable discrepancj' 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 diy 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 (which seems to be chemical rather than physical) 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.^- B3' digesting the tissue for a 



11 Fat-staining involves several principles of interest in this connection. (See 

 review by BuUard, Jour. Med. Res., 1012 (27), 55). Osmic acid (OsOj), the 

 longest used for tliis puipose, is reduced to OsOo by oleic acid, impartintr a black 

 or dark-brown color to the fat: but it does not stain saturated fatty acids, sucli 

 as palmitic or stearic acid. Thus, Christian found in pneumonic exudates fat 

 that stained by otlier methods but not by osmic acid, apparently l)ecause it con- 

 tained no oleic acid (Jour. Med. Research, 1003 (10), 100). Sudan III and 

 scarlet R {fat poyvceau) are two synthetic dyes Avhich stain fat in a purely 

 physical way, entering and remaining in the fat-droplets because tliey are nuich 

 more soluble in fat than they are in water or alcohol. (Fully discussed by 

 Michaelis (who introduced scarlet R) in Virchow's Arch., 1001 (164), 263; and 

 by Mann, "Physiological Histology," p. ."'06.) These stains have the advantage 

 of staining all sorts of fats and not staining oilier substances that may reduce 

 osmic acid. Fatty acids and soaps nmy he stained witli copper acetate, wliich 

 forms a green copper salt, and thus be distinguislied from fats ( Renda, Yir- 

 chow's Arch., 1000 (161), 104). J. Lorrain Smith (Jour. Path, and Bact., 1007 

 (12), 1) has introduced as a fat dye Nile blue sulphate, which forms a l)lue salt 

 with free fattv acids, while neutral fats are stained red bv tlie oxazone base. 



12 Bondi, Biochem. Zeit., 1900 (17), .543. 



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