NECROSIS OF TISSUES. 7 



Now, the blood contains more water than any other tissue of the 

 body. Hence the mortified part will contain more than its duo 

 proportion of water, at the expense of the healthy tissues ; it is 

 therefore all the more able to undergo solution in its own 

 fluids. 



The remaining naked-eye appearances are also due to this 

 excess of blood. For, soon after death, the colouring matter of 

 the blood deserts the corpuscles, and stains, first the serum, and 

 next all those tissues which are naturally either colourless or 

 nearly so. It saturates the walls of the vessels and the lax con- 

 nective tissue round them, so that the course of the veins may 

 be traced by the purple streaks and patches to which the livid 

 marbling of the skin in gangrene of external parts is due. 

 Finally, every part becomes equally saturated with blood, the fat 

 of the 2'><^'-nniculus adiposus not excepted. In external parts, the 

 reddish serum makes its way to the surface of the cutis. Tlio 

 previous disintegration of the rete Malpighii favours a loosening 

 of the impermeable cuticle, so that the accumulation of serum 

 may occasionally lead to the production of what are known as 

 gangrenous blebs ; more commonly, however, it simply strips off 

 the cuticle in large shreds. In the latter event, unless evapora- 

 tion be otherwise checked, a rapid desiccation of the most super- 

 ficial parts — of those which are open to the air — takes place. 

 Impregnated as they are with blood pigment, they present, when 

 dried, a very dark, nearly black colour (Grangraena sicca; 

 mummification.) Putrefactive changes are temporarily arrested 

 wherever desiccation has occurred. Desiccation, therefore, is at 

 once a means of killing living parts, as we see whenever a scab 

 is formed, and of protecting parts already dead from further 

 decay. The following statements, therefore, concerning gan- 

 grenous changes in tissue, are all conditional on the presence of 

 water in sufficient quantity for the solution of the parts ; they 

 apply, therefore, to gangrene of internal parts, and to that of 

 external parts, in so far as these are not exposed to desic- 

 cation. 



§ 11. The blood is the first of the tissues to undergo decom- 

 position. A few Avords are enough to describe the morphological 

 phenomena of the process. I have already said that the blood 

 pigment forsakes the corpuscles and is gradually imbibed by all 

 the tissues of the mortified part. We shall have to trace its 



