>n AN AMERICAN TEXT- HOOK OF PHYSIOLOGY. 



Collagen. — This is the chief constituent of the fibres of connective tissue, of the 

 organic matter of bone (ossein) and is likewise one of the constituents of cartilage. Col- 

 lagen is insoluble in water, dilute acids and alkalies. On boiling with water it forms 

 gelatin through hydration, which is soluble in hot water, but gelatinizes on cooling (as in 

 bouillon). Dry gelatin .-wells when broughl into cold water. By continuous boiling or by 

 gastric or tryptic digestion further hydration takes place with the formation of soluble 

 gelatin peptone. Gelatin fed will not take the place of proteid, but. like sugar, only more 

 effectively, it may prevent proteid waste by being burned in its stead. 1 Gelatin .yields leucin 

 and glycocoll on decomposition, but no tyrosin. It therefore gives the biuret reaction, but 

 none with Millon's reagent. It contains but little sulphur. It yields about the same 

 ainido- acids as ordinary proteid. 



Elastin. — This is very insoluble in almost all reagents and in boiling water. On 

 decomposition it yields leucin, tyrosin, glycocoll, and lysatin. It is slowly hydratcd by 

 boiling with dilute acids, and by pepsin hydrochloric acid. It contains very little sulphur, 

 and gives Millon's test. It is found in various connective tissues, and especially in the 

 cervical ligament. 



Keratin and Neuro-keratin. — These are insoluble in water, dilute acids and alkalies; 

 insoluble in pepsin hydrochloric acid, and alkaline solutions of trypsin. Keratin is found 

 in all horny structures, in epidermis, hair, wool, nails, hoofs, horn, feathers, tortoise-shell, 

 whalebone, etc. Neuro-keratin has been discovered in the brain, and in the medullary 

 sheath of nerve-fibres. 2 On decomposition with hydrochloric acid keratin yields all the 

 products given by simple proteids. It contains more sulphur than simple proteid and 

 yields more tyrosin. Drechsel 3 believes that it is transformed from simple proteid by the 

 substitution of sulphur for some of the oxygen and of tyrosin for leucin or other amido- 

 acid. Part of the sulphur is loosely combined, and a lead comb turns hair black, due to 

 the formation of lead sulphide. There are different keratins, and their sulphur content 

 varies greatly. 



Histon. — Iliston is a proteid split off from yeast nuclein and the nuclein of the white 

 blood-corpuscles and blood plates. Kossel has suggested that it is a combination of pro- 

 teid and protamin, which the investigations of Bang * tend to confirm. 



Protamins and Remarks on the Theoretical Composition of the 

 Proteid Molecule. — The protamins have been discovered in fish-sperm 

 united with nucleic acid. According to Kossel, protamins are the simplest 

 proteids. They till give the biuret test. On heating with dilute acid or in 

 tryptic digestion they are converted into protone (protamin peptone), and 

 then they break up into amido acids. Several protamins have been dis- 

 covered. That obtained from sturgeon-sperm is called sturin, from the 

 herring, clupein, from the salmon, salmin, and from the mackerel, scombrin. 

 Sturin, according to Kossel, 5 breaks up as follows ; 



C 36 H fi9 N 19 7 + 5H 2 = C 6 H 9 N 3 2 + 3C 6 H M N 4 2 + C 6 H 14 N 2 2 



sturin. Ilistidin. Axginin. I.ysin. 



Kossel'- investigations show thai salmin and clupein are identical and 

 yield on decomposition arginin and amido valerianic acid, while scombrin 

 also yields arginin, without any histidin or lvsin. 6 



1 Voit : Zeitnehrififui Biolopie, 1872, Bd. 8, S. 297. 



1 Kulme and Chittenden: Ibid., 1890, Bd. 26, S. 291. 



3 Ladenbuipfs Il<atihiijr/>rlnirlt <hr ( 'hrmir, lSS.j, Bd. 3 S. 571. 



* ZeiUchrift fw phyaiologuche Chemie, 1899, Bd. 27, S. 463. 



5 Deutsche medicini8che Wochensehrift, 1898, No. 37. 



6 Zeitschrifi fiir physiologischc Chemie, 1899 Bd. 26, S. 588. 



