834 GENERAL PHYSIOLOGY 



which lives in the Mediterranean Sea, be brought into the air, the 

 thick, hard skin begins gradually to liquefy into a viscous mucus, 

 and after a few hours becomes completely softened. If small pin- 

 holes be bored through an excised piece of the skin this mucous 

 liquefaction, as Semper ('68) showed, can be rapidly induced ; around 

 each hole the cells begin at once to swell up and disintegrate, and 

 the whole piece is changed finally into a thick liquid mass, which, 

 when touched, can be drawn out into glistening threads. Many 

 species of the holothurian genus Stichopus are said to transform 

 their skin in a very short time into a thick mucus. It would 

 be extremely interesting to investigate both chemically and micro- 

 scopically this wholly unique case of a sudden mucous meta- 

 morphosis of so solid and tough a structure as is the holothurian 

 skin. Krukenberg ('82) alone has made a partial study of it. The 

 mucous metamorphosis of epithelium-cells, leucocytes, etc., which 



occurs in the human body, es- 

 pecially in intense catarrhs, is well 

 known : in these cases the cells in 

 question die with a swelling and 

 transformation of their living sub- 

 stance into mucus (Fig. 147). 



In the phenomena of amyloid 

 metamorphosis, in contrast to the 

 FIG. i47.-Mucous-metamorpho 8 ed ceils. /, processes hitherto considered, a 

 Leucocytes ; ii, ciliated cells. (After substance is formed which, so far 



as is known, does not occur at 

 all in the normal body. This 



.substance, which glistens like wax or lard which probably has 

 conferred upon the disease in question the name of waxy or 

 lardaceous degeneration was first termed by Virchow amyloid 

 substance, because with iodine staining it behaves like plant-amylum 

 .and cellulose, under certain conditions being coloured blue by the 

 iodine. Later it was recognised as a proteid-like body, for it 

 contains nitrogen and gives certain proteid reactions ; hence, for 

 the present it is classed in the comprehensive group of albuminoids. 

 Its behaviour with the aniline colour, methyl violet, is very 

 characteristic; with it it takes on a beautiful ruby-red colour, 

 while healthy tissues are coloured blue. By its character as an 

 .albuminoid, amyloid substance points plainly to its origin. It can 

 be derived only from the proteids of the cell, and, although thus 

 far nothing is known in detail concerning its origin, it may safely 

 be considered as a metamorphosed proteid, which is excreted to 

 the outside by the cell and stored up. It never seems to be stored 

 within the cell itself, it is always found rather in the connective 

 substances cementing the cells, especially in the walls of the small 

 blood-vessels (Fig. 148). But, in proportion as the cells secrete 

 it, they die, whether as the result of perverse metabolism, the 



