386 RETROGRESSIVE CHANGES 



The abundance of fat in caseous material on microscopic exami- 

 nation is very striking. In addition to the figures obtained by Caldwell, 

 Bossart^^ found from 13.7 per cent, to 19.4 per cent, of the dry sub- 

 stance of caseous material soluble in alcohol and ether. In the scrap- 

 ings from tuberculous bovine glands I have found 22.7-23.9 per cent, 

 of the organic material soluble in alcohol and ether. ^^ Of this soluble 

 material, Bossart found 25 to 33 per cent, of cholesterol, and Leber^'* 

 found 38.31 per cent., which is a much higher phospholipin pro- 

 portion than Bossart detected. Caldwell found cholesterol higher 

 and phospholipins lower in caseous than in normal tissues. The 

 total amount of lipins, however, constituted a smaller percentage of 

 the dry weight than in the normal tissues from which the caseous 

 material originated. Presumably these fatty materials are derived 

 chiefly from the disintegrated cells; this is probably true of the phos- 

 pholipin and cholesterol, but the fact that in histological preparations 

 most of the fat is found about the periphery of the caseous area,^^ sup- 

 ports the belief that it has wandered in from the outside.^® A certain 

 proportion of the fat is possibly derived from the bodies of the tubercle 

 bacilli, which usually contain about 40 per cent, of fatty matter; but 

 it has not been determined whether the fat from this origin forms an 

 appreciable part of the fatty matter of caseous material. 



Caseous areas persist for extremely long periods of time without 

 undergoing absorption, which indicates that the autolytic enzymes 

 are destroyed early in the process, presumably by the toxins of the 

 tubercle bacillus; corresponding to this Schmoll found autolj'sis very 

 slight indeed in caseous areas, and even when the caseous material 

 breaks down to form a "cold abscess" the fluid differs from true pus 

 in containing less free amino-acids, e. g., tyrosine is missing." Caldwell 

 also obtained lower figures for extractives in caseous than in normal 

 tissues. Because of a lack of chemotactic substances no leucoc3'tes 

 enter to remove the dead material, in consequence of which caseous 

 material gives no evidence of containing proteases, according to the 

 Miiller-Jochmann plate method. That the failure of absoprtion is not 

 due to a modification of the proteins into an indigestible form is 

 shown by the rapid softening of caseous areas when, through mixed 

 infection, chemotactic substances are once developed and leucocytes 

 enter. Jobling and Petersen^^ suggest that in caseation the autolysis 

 is inhibited by the soaps of fatty acids, which are abundant in caseous 

 areas and have a marked antitryptic effect. 



^* Quoted by Schmoll, loc. cit.^ 

 " Wells, Jour. Med. Research, 1906 (14), 491. 

 ^* Quoted by Schmoll.^ 

 1^ Sata, Ziegler's Beitr., 1900 (28), 461. 



^^ Fischler and Gross (Ziegler's Beitr., 1905 (7th suppl.), 344) could find no 

 fatty acids in caseous areas bv histological methods, 

 i' See Muller, Cent. inn. Med., 1907 (2S), 297. 

 IS Jour. Exp. Med., 1914 (19), 239; Zcit. Immunitat., 1914 (23), 71. 



