i LIVING MATTER 25 



Glucoproteins are conjugated proteins, consisting of a carbo- 

 hydrate radicle combined with protein. The nature and consti- 

 tution of this carbohydrate group is unknown. It appears to be 

 a polysaccharide, since it does not reduce : it contains an amino 

 group (NH 2 ), for when boiled with acids, it usually yields gluco- 

 samine. 



The group of proteins known as the scleroproteins includes a 

 series of substances which have few physical properties in common 

 with the preceding groups, but share many other characters with 

 them. They never form part of the animal cell, but compose the 

 skeletal or supporting substance for the cells and organs of the 

 body: they belong to the histological group of the connective 

 tissues in the widest sense of that term. There are no sclero- 

 proteins in the tissue fluids of animals' blood, lymph, etc. The 

 concept scleroprotein is essentially morphological, and from a 

 chemical point of view includes most various bodies. 



As proteins, the scleroproteins have many properties in common 

 with the other groups. By the action of acids or of proteolytic 

 ferments they are split into proteoses, peptones, and amino-acids ; 

 they form salts ; and they have the same percentage composition 

 and give the same colour reactions. 



Of the various scleroproteins enumerated in the table, we may 

 say that collagen is the general substance of bone, cartilage, and 

 connective fibres ; on boiling, it takes up water and is transformed 

 into gelatin. Keratin, the ground substance of the cornea, is an 

 elaboration product of the epidermic cells of the cutis. Elastin, a 

 component of the fibres of elastic tissue and the ligamentum 

 nuchae, is a product of connective tissue cells. Fibroin, the 

 principal component of silk, is an elaboration product of the 

 spinning gland of the silkworm. Spongin is the organic support- 

 ing substance of the bath sponge. Conchiolin is the organic matrix 

 of the snail and other molluscs. Amyloid, lastly, is a substance 

 which is absent in the healthy organism, but accumulates in 

 enormous quantities under the influence of various pathological 

 degenerative processes. 



Albumoid is the name which has been given to many different 

 substances found in various organisms, e.g. the membrana propria 

 of certain glands, the vitreous membrane, sarcolernma, the solid 

 constituents of the lens, scales of fishes, etc. These are also 

 scleroproteins. 



Lastly, the group of pigments, or melanins, includes all those 

 various pigments, brown, black, chestnut, etc., which determine 

 the characteristic hue of hair, fur, and choroid, and which are found 

 in the so-called melanotic tumours. 



VIII. The analytical and experimental work on the chemical 

 structure and constitution of proteins, as recently carried out by 

 such distinguished physiological chemists as Kossel, Hofrneister, 



