60 THE GELATIN FROM WHITE 



free from sulphur, or hold at least that this element is an 

 unessential constituent of the molecule.* 



In all of these tissues the difficulty of isolating with perfect 

 purity the albuminoid itself is very great. In white fibrous 

 tissue, for example, the close juxtaposition of the several 

 anatomical elements, as well as the similarity in the reactions 

 of the several chemical substances present, make it an 

 exceedingly difficult matter to insure a complete isolation of 

 the collagen. In a general way this may be readily done, but 

 to obtain collagen from tendons, for example, absolutely free 

 from all traces of mucin, elastin, and albuminous matter is not 

 so easy. To be sure, the large proportion of collagen present 

 in tendons practically insures, with reasonable care, freedom 

 from any very large percentage of impurity ; but it is generally 

 understood among physiological chemists that the sulphur of 

 collagen or gelatin, for example, is somewhat questionable, 

 that at least a portion of the 0.6 per cent of this element 

 usually accredited to gelatin may be due to admixture of the 

 richer sulphur-containing bodies, mucin or albumin, with 

 which it is so intimately associated in the tissue. Indeed, it 

 seems doubtful if we have on record any analysis of collagen 

 or gelatin extracted from white fibrous connective tissue 

 which can be accepted as representing the chemical composi- 

 tion of the perfectly pure substance. Thus, a glance through 

 the literature of the subject shows that most of our knowledge, 

 especially bearing on the chemical composition of gelatin, is 

 based upon a study of the commercial product, the source of 

 which is obviously more or less uncertain. It has therefore 

 seemed to the writer very desirable, in view of the probable 

 existence of a number of distinct collagens and gelatins, to 

 determine as accurately as possible the chemical composition 

 of gelatin from white fibrous tissue, having especially in view 

 the preparation of the substance entirely free from all traces 

 of elastin, mucin, and albumin. This seems the more important 

 as a necessary step preliminary to comparing the reactions of 



* Kecherches BUT la constitution des matieres collagenes. Comptes rend us, 

 t Ixxxii, p. 262. 



