THE ALBUMINOID BODIES. 461 



contained principally in the connecting and protecting structures of the body. 

 They can enter into combination with acids or alkalies. 



1. Keratin is present in all horny and epidermal structures. It is soluble only 

 in boiling caustic alkalies, while it swells in cold alkalies and in concentrated 

 acetic acid. It contains from 2 to 5 per cent, of sulphur, a large part of which 

 can be split off by alkalies. It is indigestible; decomposed by hydrolysis it yields 

 10 per cent, of leucin and 3.6 per cent, of tyrosin. Neurokeratin is described on 

 p. 627. 



2. Fibroin is soluble in strong alkalies and mineral acids, as well as in cupric- 

 ammonium sulphate. Boiled with sulphuric acid it yields 5 per cent, of tyrosin, 

 leucin and glycin. It is the principal ingredient of the web of insects and spiders. 

 By long boiling silk-gelatin (sericiri) is obtained from silk. This body is richer in 

 oxygen and water than fibroin. Treated with sulphuric acid it yields, in addition 

 to leucin and tyrosin, also serin, a crystalline amidoacid. 



3. Spongin, a body resembling fibroin, and derived from sponges, yields leucin 

 and glycin as decomposition-products. 



4. Elastin, the ground-substance of all elastic tissue-elements, is soluble only 

 when boiled in concentrated potassium hydroxid. It yields from 36 to 45 per 

 cent, of leucin, together with one-half per cent, of tyrosin. It yields the reactions 

 of albumin and its decomposition-products. It contains sulphur only in loose 

 combination. It is peptonized by trypsin, but not by the gastric juice. 



5 . Glutin or bone-gelatin can be prepared from all connective or gelatin-yielding 

 substances (which contain collagen) in the form of gelatin by boiling with water. 

 This gelatin on cooling forms a jelly. Collagen is soluble by boiling with acids 

 or alkalies. Glut in is strongly levorotatory. It is transformed by long boiling 

 and digestion into a peptone-like state, in which it does not become gelatinous. 

 A glutin-like body is present in leukemic blood and in splenic juice. Glycin, 

 leucin and ammonia, but no tyrosin, result on hydrolytic decomposition. 

 Glutin contains 0.7 per cent, of sulphur. 



6. Chondrin or cartilage-gelatin is obtained by boiling hyaline cartilage. It 

 becomes gelatinous in the cold. It is precipitated by acetic acid and by small 

 amounts of mineral acids. It is dissolved in an excess of the latter as well as by 

 neutral salts. 



The true characteristic substance of hyaline and elastic cartilage is a mono- 

 basic acid, namely, chondroitin (Ci 8 H 27 Npi 4 ) , which as an ethereal sulphate, namely, 

 as chondroitin-sulphuric acid, is contained in cartilage. This acid is present in 

 cartilage only in exceedingly loose combination with albuminous or gelatinous 

 substances. Alkalies separate the albuminous bodies from the chondroitin-sul- 

 phuric acid by forming alkaline salts with the latter. The chondrin (of the earlier 

 writers) is a gelatinizing solution consisting of a mixture of ordinary gelatin and 

 the last-mentioned chondroitin-sulphates of the alkalies. It can, therefore, be 

 prepared artificially from gelatin and potassium or sodium chondroitin-sulphate. 

 True hyaline cartilage is, therefore, distinguished from (gelatin-yielding) osseous 

 cartilage by the circumstance that the ground-substance of the former contains 

 chondroitin-sulphates. 



On decomposition of chondroitin (as well as of chitin) glycosamin (C 6 H n O 5 NH 2 ) 

 is formed, the latter on treatment with nitrous acid being transformed into glucose 

 an example of the manner in which non-nitrogenous carbohydrates may be 

 derived from nitrogenous albuminous bodies. 



7. The hydrolytic ferments, also designated enzymes (in order to distinguish 

 them from the organized ferments, for example yeast and bacteria). The charac- 

 teristic of all organized ferments is that they are active only in the presence of 

 water and in such a manner that they cause a decomposition of the body upon 

 which they act as a result of which the latter takes up water. All of the ferments 

 likewise decompose hydrogen dioxid into water and oxygen. Their activity is 

 greatest at a temperature between 30 and 35 C. They are destroyed by boiling. 

 In the dry state they may tolerate exposure to a temperature of 100 C. without 

 attenuation. The addition in considerable amount of antiseptics that destroy 

 lower organisms does not check their activity. During periods of protracted in- 

 activity their solutions undergo destruction in greater or lesser degree. The fol- 

 lowing hydrolytic ferments are distinguished: 



(a) Sugar-forming ferments in the saliva, the pancreatic juice, the intestinal 

 juice, the bile, the blood, the lymph, the chyle, the liver, the urine, the milk, 

 and invertin in the intestinal juice. 



Almost all dead tissues, organic fluids, and even albuminous bodies, may 



