424 RETROGRESSIVE CHANGES 



This carries out the resemblance of amyloid to nucleoproteins, and, 

 likewise, Neuberg found amj-loid very slowly digested bj^ pepsin, and 

 much better by trypsin, although less rapidly than simple protein; it 

 is also destroyed by autolytic enzymes, for amyloid tissues readily 

 undergo autolysis. ^^ Neuberg considers, from the above results, that 

 amyloid is probably a transformation-product of the tissue protein, 

 similar to the transformation of simple proteins into protamins that 

 occurs in the testicle of spawning salmon as they go up the streams, 

 as shown by Miescher's classical studies. Raubitschek'*° found that 

 isolated amyloid, when used for immune reactions, behaved like a 

 specific protein, different from the normal proteins of the animal from 

 whence it came and apparently biologically the same in different spe- 

 cies. (This observation awaits confirmation.) 



Krawkow considers that amyloid differs from normal chondroitin- 

 sulphuric acid compounds, such as cartilage, in that in the latter the 

 acid radical is in a loose combination with the protein, while in amy- 

 loid the combination is a very firm one, perhaps in the nature of an 

 ester. The occurrence of the typical amyloid reaction in what ap- 

 pears otherwise to be normal cartilage, occasionally observed in senile 

 tissues, may be due to the transformation of loosely bound into firmly 

 bound chondroitin-sulphuric acid. In any event, amyloid is not essen- 

 tially a pathological product, but rather a slightly modified normal 

 constituent of the body. However, in view of the contradictory results 

 of Hanssen and Mayeda, as yet uncontroverted, the chemical nature of 

 amyloid must be considered as undetermined. An important con- 

 sideration is that amyloid deposition occurs under similar conditions 

 in all sorts of animals, including birds; it is very often found in the 

 livers of antitoxin horses, and mice are especially prone to a severe 

 amyloidosis after relatively slight and brief infectious processes. ^^ 



Staining Properties. — The classical reaction for amyloid is its staining a reddish 

 brown when treated with iodin (best as Lugol's 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. Occasionally 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. Oc- 

 casionally an otherwise typical amyloid will fail to react to iodin, but will stain 

 well witii 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 bj' splenic amyloid. These variations probably dejjcnd 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 



^* Concerning the absorption of amyloid see Dantchokow, Virchow's Archiv., 

 1907 (187), 1. 



"Verh. Dcut. Path. Gesell., 1910 (14), 273. 



" See Finzi, Lo Speriment., 1911 (05), 483; Davidsohn, Virchow's Arch., 1908 

 (192), 22(). 



