THE ALBUMINOIDS. 57 



of Osborne that this property is referable to the nucleinic acid com- 

 ponent. As would be expected, the degree of dextrorotation is 

 greater in the nucleins than in the corresponding nucleoproteids. 



The Haemoglobins. The group of the haemoglobins is essen- 

 tially represented by the common blood-pigment of vertebrate 

 animals, viz., hemoglobin. Closely related to it is the so-called 

 hsemocyanin, which is found in crabs and other invertebrates, and 

 the chlorophyll of plants. The haemoglobin has been studied with 

 special care, and we now have a fairly clear idea of its structure. In 

 it an albuminous radicle belonging to the histon group, viz., globin, 

 is combined with the iron-containing pigment haematin. Both, as 

 also the haemocyanin, will be considered in detail in the section on 

 the blood, where the chemical relation of the blood-pigment to the 

 common respiratory pigment of the plant will likewise be pointed 

 out. 



THE ALBUMINOIDS. 



While the albumins and proteids, which have been considered in 

 the foregoing pages, are essentially constituents of the animal cell, 

 viz., nucleus and protoplasm, the albuminoids or ylutinoids, as they 

 are also termed, represent the principal components of the intercel- 

 lular structures. They are thus largely found in the supporting 

 tissues of the body, viz., the connective tissue, cartilage, and bone. 

 In the nutritive fluids, viz., blood and lymph, they do not occur. 

 The group comprises the collagens or glutins, certain vegetable 

 albuminoids, reticulin, elastin, the ichthylepidin of fish scales, 

 various substances which have been found in the supporting struct- 

 ures of invertebrates, and which are collectively termed skeletins 

 (fibroin, sericin, spongin, conchiolin, cornei'n, elastoidin) and amy- 

 loid, which is a pathological product and not normally encountered 

 in the body. The keratins have also been classed as albuminoids 

 in the past, but there is a tendency at present to regard them as 

 true albumins and as such they have been considered in this work. 



The albuminoids are albuminous derivatives, which are produced 

 in the body from albumins through cellular activity. As a class 

 they do not contain all the typical radicles of the albumins, while 

 in some certain complexes are more largely represented. The col- 

 lagens thus differ from the true albumins in the absence of the cystin 

 and carbohydrate group ; they further lack the tyrosin and trvpto- 

 phan group ; elastin, fibroin, and sericin lack the glutaminio acid 

 radicle, etc. Collagen, on the other hand, contains much more glyco- 

 coll than the true albumins. 



The nutritive value of the albuminoids is distinctly less than that 

 of the albumins. Voit has shown that gelatin (glutin), for example, is 

 not capable of maintaining life. Certain members of the group, 

 moreover, cannot be regarded as food-stuffs in any sense owing to 

 the extreme resistance which they offer to most solvents, including 

 the digestive fluids. All albuminoids in fact arc insoluble in the 



