TENDONS, LIGAMENTS, SKIN. 417 



position. They are firm and elastic, are not changed by cold 

 water, nor dissolved by acetic acid; the latter reagent renders 

 them gelatinous and tough, but takes up no protein-compound. 

 The organs containing this tissue diminish when boiled, become 

 harder and more rigid, but ultimately soften and dissolve into 

 gelatin, forming a solution that stiffens on cooling. Alcohol, 

 ether, and oil exert no action on cellular tissue, even when aided 

 by heat. 



Tendons swell on being boiled, become yellow, and are gra- 

 dually converted into gelatin. The solution is turbid in con- 

 sequence of the flocculent appearance presented by minute 

 vessels in suspension. In concentrated acetic acid they swell, 

 become transparent and gelatinous, and in this state readily 

 dissolve in hot water, from which neither an alkali nor ferro- 

 cyanide of potassium throws down any precipitate. 



Ligaments consist partly of cellular and partly of elastic 

 tissue, and these two structures present both chemical and 

 physiological differences. True elastic tissue is not changed by 

 acetic acid, is not converted by boiling into gelatin, but with 

 the aid of heat dissolves readily in dilute mineral acids, from 

 which it is not precipitated by ferrocyanide of potassium. As 

 illustrations of the true elastic tissue we may refer to the liga- 

 menta flava between the vertebrae and the ligamentum nuchse 

 in the ruminants. 



The cutis, or true skin, is a contractile cellular tissue con- 

 vertible, by boiling, into gelatin. It is permeated by a fluid, and 

 contains also cellular tissue and vessels. Wienholt has endea- 

 voured to determine their relative proportions; he obtained: 

 Cutaneous tissue (including cellular tissue and vessels) . 32-53 

 Water ..... 57'50 



in which were dissolved : 



Albumen , . . . .1-54 



Alcohol-extract ..... 0-83 

 Water-extract ..... 7-60 



The skins of different animals require boiling for different lengths 

 of time in order to be converted into gelatiD, and the change 

 is effected more rapidly in young than in old animals. 



The conversion of the cutis into gelatin is much facilitated 

 by the action of dilute alkalies or acids ; it then takes place at 

 an ordinary temperature. The skin combines with basic sul- 

 phate of iron, and with bichloride of mercury, when immersed in 



ii. 27 



