CHEMICAL BASIS OF THE ANIMAL BODY. 1203 



Papin's digester, is converted into true gelatin. During the 

 conversion an extremely insoluble residue is formed which has 

 affinities on the one hand with keratin and on the other with 

 elastin. 



Elastin. 



This is the characteristic component of the elastic fibres 

 which remain after the removal of gelatin, mucin, fats, etc., 

 from tissues such as "ligamentum nuchse." Some of the more 

 important ways in which it differs from the substances which 

 have been previously described are sufficiently stated by describ- 

 ing the method of its preparation in a pure form. Ligamentum 

 nuchas of an ox is cut into fine slices, treated for three or four 

 days with boiling water, then for some hours with 1 p.c. caustic 

 potash at 100° C. and subsequently with water. This process is 

 then repeated with 10 p.c. acetic acid. Finally it is treated 

 for 24 hours in the cold with 5 p.c. hydrochloric acid, washed 

 with water, boiled with 95 p.c. alcohol and extracted for at 

 least two weeks with ether to remove every trace of adherent 

 fat. By the above method it may be obtained as a pale yel- 

 lowish powder in which the shape of fragments of the original 

 elastic fibres may be still distinguished under the microscope. 

 When moist it is yellow and elastic, but on drying it becomes 

 brittle and may with difficulty be pulverized in a mortar. 

 Sulphur probably does not enter into its composition (?). It 

 may be dissolved by strong alkalis at 100° C, and it also goes 

 into solution when treated with mineral acids at the same tem- 

 perature ; but in the latter case the solution involves decompo- 

 sition with the formation of much leucine (30 — 40 p.c.) and 

 traces (-25 p.c.) of tyrosine when the acid employed is sul- 

 phuric. If strong hydrochloric acid be employed with chloride 

 of zinc the same crystalline products are obtained together with 

 ammonia, glycine, and an amidovalerianic acid, but no glutamic 

 or aspartic acids. In this respect it differs from both ordinary 

 proteids and gelatin, since the former when similarly treated 

 yield the glutamic and aspartic acids but no glycine, and 

 the latter never yields the least trace of tyrosine. During the 

 putrefactive decomposition of elastin products similar to the 

 above are obtained together with some peptone-like substance. 

 When treated with superheated water, or with dilute hydro- 

 chloric acid at 100° C. or with pepsin or trypsin in acid and 

 alkaline medium respectively, elastin is more or less rapidly 

 dissolved and undergoes a true digestive change, during which 

 products are formed, many of whose general reactions are anal- 

 ogous to those of the digestive products of proteids. It is 

 however as yet uncertain whether a true elastinpeptone can be 

 obtained ; it is more probable that during the digestion only 



