46 THE ALBUMINS. 



spinal-uphill, from the spirographic membrane ; the holothuriun 

 miiein ; the chondrosin of certain mushrooms; and others. The 

 hyalin which is I'ouml in echinocoecns cysts, and the onuphiu of 

 the tubes of Onnpliis tubicola, which have both been regarded as 

 hyalogens, arc apparently not proteids. Hyalins can, however, also 

 occur as nidi, or as closely related bodies which are not combined 

 with an albuminous group. They are principally found in the 

 extra-skeletal or intra-skeletal parts of various animals. Among 

 these may be mentioned the so-called chondroitin, which occurs in 

 the matrix of the cartilage of the higher animals, as chondroitin- 

 s*ulphuric acid ; and chitin, which forms the greater portion of the 

 carapace of the arthropods and the inner skeletal structures of cer- 

 tain cephalopods and brachiopods. From both these substances 

 glucosamin can be obtained on hydrolytic decomposition. 



The hyalogens are for the most part insoluble in water, and, as we 

 have seen, are decomposed by treating with dilute alkaline solutions. 

 They give the general color-reactions of the albumins, and, like the 

 mucins and mucoids, consist of carbon, hydrogen, nitrogen, oxygen, 

 and sulphur. Their albuminous radicles, however, are unknown. 



Of the phosphoglucoproteids little is known. They are appar- 

 ently related to the nucleo-albumins, and yield paranuclein on diges- 

 tion with artificial gastric juice. 



The haemoglobins are essentially compounds which contain an 

 albuminous radicle that is variously combined with an organic 

 pigment. They will be considered in detail in the chapter on the 

 Blood. 



THE ALBUMINOIDS. 



The albuminoids, as they are commonly termed, are closely related 

 to the albumins, but differ from these in many important par- 

 ticulars. For the most part, they contain less carbon and more 

 oxygen than the albumins proper, and can hence be regarded as 

 early products of decomposition and oxidation. They are not 

 found in the vegetable world, and must therefore be produced in 

 the animal body through a certain rearrangement of atoms from 

 the vegetable albumins. During the reconstruction of the molecule 

 in the animal body, however, a certain amount of carbon is mani- 

 festly lost. We find, as a matter of fact, that in certain representa- 

 tives of this group the aromatic radicle is lacking, and among the 

 decomposition-products of such substances we accordingly find 

 neither indol nor ty rosin. Their nutritive value is therefore also 

 less than that of the albumins, and Yoit actually demonstrated that 

 gelatin, for example, is in itself insufficient to maintain life. Certain 

 members of this group, moreover, cannot be regarded as food-stuffs 

 at all, owing to the extreme resistance which they offer to most 

 solvents, including the digestive fluids. 



As a class the albuminoids occur widelv distributed in the animal 



