Ageing of Elastic Tissue 91 



Two dimensional paper chromatography appears to be an 

 effeetive means of characterizing elastin. After complete 

 hydrolysis, tryptophane exists as a trace in elastin (Lansing 

 et al., 1951) but is a significant component of other tissue 

 proteins. By tracing the disappearance of the ninhydrin 

 colorized tryptophane spot in the chromatogram one can 

 readily determine when contaminants of elastin are removed. 

 This w^as done in the NaOH digestion series and it was 

 determined that the tryptophane spot disappeared after 

 forty to fifty minutes. At this time, glycine, proline, leucine, 

 isoleucine and valine were readily identified in the chromato- 

 gram and minor spots for aspartic and glutamic acid were 

 present. The finding of these amino acids as the principal 

 components of elastin is consistent with published analytical 

 data for the amino acid composition of elastin (Neuman and 

 Logan, 1950). 



There w^as a progressive reduction in the amount of residual 

 material through forty to forty-five minutes of digestion, after 

 which time the residual dry weight was constant through 

 sixty minutes. These data seem to indicate that digestion of 

 elastic tissue in hot, dilute alkali for less than forty-five 

 minutes is not adequate to remove extraneous materials from 

 the tissue (Fig. 1). 



Microscopic examination of samples digested in NaOH for 

 time periods less than forty-five minutes revealed variable 

 amounts of collagen and muscle after staining with Mallory's 

 procedure. At and after forty-five minutes no collagen or 

 muscle could be demonstrated and the elastin was optically 

 homogenous, refractile, and apparently free from contami- 

 nating structures. Likewise, elastin prepared from ligamen- 

 tum nuchae was free of collagen in so far as could be determined 

 by light microscopy and electron microscopy. It w^as bire- 

 fringent when stretched, or dried, had a refractive index of 

 1 • 534, was resistant to digestion by crystalline trypsin 

 (Armour) and stained effectively with orcein, resorcin- 

 fuchsin, or the Verhoeff procedure. 



