350 RETEOGEESSIVE PROCESSES 



but rather a slightly modified normal constituent of the 

 body. 



Staining Properties. The classical reaction for amyloid 

 is its staining a reddish brown when treated with iodin (best as 

 LugoPs solution) in the fresh state. Such stained specimens, 

 if afterward treated with dilute sulphuric acid, usually become 

 blue or greenish, but may merely turn a deeper brown. Occa- 

 sionally old compact amyloid may stain bluish or green with 

 iodin alone. The iodin reaction disappears in specimens that 

 have been kept for some time in preserving fluids, or in tissues 

 that have become alkaline, and is generally less persistent than 

 the metachromatic staining by methyl-violet or methyl-green, 

 which color the amyloid red. Occasionally an otherwise typical 

 amyloid will fail to react to iodin, but will stain well with 

 methyl- violet. All these variations may occur in different 

 specimens from the same body, and the blue iodin-sulphuric 

 acid reaction is usually given well only by splenic amyloid. 

 These variations probably depend upon the age and stage of 

 development of the amyloid, or upon secondary alterations, and 

 are perhaps related to Neuberg's observations on the difference 

 in composition of amyloid of different origins. 



Krawkow studied these reactions with pure, isolated amyloid, 

 and found evidence that the iodin reaction depends upon the 

 physical properties of the amyloid, while the methyl-violet 

 stain is a chemical reaction, and hence the iodin reaction is 

 much the more readily altered or lost. As Dickinson l says, 

 amyloid stains w r ith iodin simply as if it absorbed the iodin 

 more than does the surrounding tissue. The methyl-violet 

 reaction is due to the dye forming a compound with the chon- 

 droitin-sulphuric acid, for Krawkow found that these substances 

 unite with one another to form a rose-red precipitate. Schmidt 

 found that implanted pieces of amyloid lost their iodin reaction 

 as they underwent autolysis, while the methyl-violet reaction 

 was still very distinct. 2 It is evident, therefore, that iodin is 

 not by itself a specific stain for amyloid, especially as glycogen 

 gives a similar reaction, 3 while true amyloid may not react. 



1 Allbutt's System, vol. 3, p. 225. 



2 Litten (Verb. Deut. Path. Gesell., 1904 (7), 47) states that thionin and 

 kresyl-violet are the most specific stains for amyloid, which they^ color blue; 

 whereas methyl-violet stains red not only amyloid but also mucin, mast cell 

 granules, and the ground substance of cartilage, v. Gieson's stain usually 

 colors amyloid pale yellow, and hyalin red. 



3 See Wichmann, Ziegler's Beitr., 1893 (13), 487. 



