( IIKMICAL BASIS OF THK ANIMAL 1!HV. 



,ip|H-ars that th- substance at tir>t secreted by tin- mu<ou> 

 (nf Helix) may not be typical niiicin, luit a sort of mucinogen 

 whii-h readily gives rise to mucin on treatment with dilute 

 (til i .c.) caustic potash. 1 If it be assumed for tin- moment that 



is only nt- kind of mucin, then the following general state- 

 ments as to this substance may be additionally made. It is pre- 

 cipitated from its solution.-, by a<rti<- or hydrochloric acids, the 

 precipitate being soluble in excess of the latter hut not of the 

 former acid. In its precipitated form it swells up strongly in 

 water hut does not go into true solution ; the addition of dilute 

 alkalis (/I '_' p.c. ) r of lime-water lead> to its ready solution. 

 from which it can again he pie. ipitated by the addition 

 acid. It may be extracted from any mucigenous tissue hy the 



! dilute alkalis or lime-water, and in solution is somewhat 

 chnra lly precipitated hy hasic lead acetate. Our knosvl- 



"f mucin i.s ho\\e\-r in an extremely transitional condition. 



and recent investigations have shown that probably the mu<-in> 



d from ditleivnt >our<-es are really distinct substances, ju-t 



lamiliar with ditl'erent forms of proteids. From this it 



follows that no general statement of the properties of the nun-ins 



made which would he other than misleading, nnl it 



will conduce to clearne>s to ^ive a hrief account of this suhstam e 



::om each of the chief sources from which it has 



Mucin is not a constituent of normal hile 



when freshly secreted, hut is found in it as the result of the 



tory activity of the internal epithelium of the ^all-Madder. 



bait prep.i). .'. il'aijkull). liile is mixed with 



t al.-olutc alcohol and centrifiiLiiiliM'd ; the pivcjpi- 



nuicin which is thus ohtaim-d i- then dis-ol\ed in \\.itcr 



and the ahove j-nx5ess repeated two or three tiuic^. An aqueous 



solution of thi< mucin is precipitated hy acetic and hydrH-hlorie 



soluhle in excess of either acjd. and \ield- -tlon-ly 



:d reactions. This mucin dilleis from that ohtanied 



from otli. in not yielding any ledu.-in^ siil.-tam ,- when 



hoiled witii acids, and in the soluhil-ity of its precipitate obtained 



hy n. acetic acid in an excess of this acid. It also con- 



phosphoms, and is by some regarded aa more closely alli.-d 



to the niicleo-all.iimins (see p. 89) than to the true nui- 



'he 8vb-maxill>i r;i <//.'/j// 3 Tin- -l.md ii finely 

 minc.-d. washed, and extracted with \\.itrr: the ext ItOM 



,. 1'll.u-. rV 190. 



.i. f. P.VM../. Cktm, IM. % |I*I).S 171. Mil I I HH.I). S III 



ktlll. Ibid. MI 



llm.M /: i*AyW. Ckfm. xii. (18a). 8. 1. Com.. 



otln-r lit.-r:itiir.- ilH,|..|i.k%. Il.. ( ,|,.. S.-\|. r - mrti.-chrm. Unteri. lift. 4 { 1 87 1 ), 8. 590. 



>>. ii,r n. n:i 



