120 PHYSIOLOGY 



Other members of this group are fibroin, which forms the main 

 substance of silk, spongin, the horny framework of sponges, concJiiolin, 

 the ground substance of shells, and perhaps the amyloid substance or 

 lardacein which we have already mentioned in connection with the 

 mucoids. All these sclero-proteins present considerable differences 

 in their qualitative and quantitative composition in amino-acids. Their 

 proximate composition is shown in the Table on the preceding page 

 (Abderhalden). 



We have finally to mention a miscellaneous collection of bodies 

 which are allied to the proteins and are distinguished by their extreme 

 insolubility. They are often designated as albumoids. Of their com- 

 position we know practically nothing. Under this name are grouped 

 such substances as those forming the membrana propria of glands, the 

 sarcolemma of striated muscle, the albumoid of the crystalline lens, 

 the ground substance of the chorda dorsalis, the organic basis of fish 

 scales, and many similar substances. In every case the substance is 

 characterised necessarily according to its place of origin, little or 

 nothing being known as to its chemical composition. 



