CHEMICAL SCIENCE. 245 



killed the living tissue, acts afterwards as a powerful antiseptic or preserva- 

 tive of it. 



It is not within my province to point out to those extensively employing 

 caustics, to whom these facts may be new, the importance of bearing in 

 mind this distinctive feature between the two classes of caustics, when select- 

 ing the description of caustic to be employed in any given case. 



Although caustics may be conveniently divided in the manner described 

 into two principal classes, these classes can be further subdivided into many 

 others, because the mode of action is frequently distinct in each individual 

 case, whatever the final result may be on the living tissue. 



To illustrate this point, the modes of action of caustic potash and chromic 

 acid may be cited. When the living tissue is placed in contact with caustic 

 potash, the destruction of its vitality ensues by the potash dissolving its 

 albuminous and fibrinous components ; in fact, acting in the manner de- 

 scribed by chemists for obtaining the various protein substances from organic 

 matter. Of course I only allude to the leading features of the action of caus- 

 tics in this instance as well as in others. When the same tissue is treated, 

 chromic acid, instead of obtaining a solution of the protein compounds of 

 the tissue, and thus destroying its organized structure, the tissue is destroyed 

 by a slow process of combustion; or, in other words, it is oxidized at the 

 expense of the oxygen of chromic acid, by reason of the facility with which 

 that acid parts with its abundant oxygen when in contact with organic 

 bodies. The manganese with potash acts in a similar way as a caustic to 

 chromic acid, but in consequence of the permanganic and manganic acids 

 which it contains being in combination with the base potash, its action is 

 more controllable and persistent. It may not be here out of place to men- 

 tion, what appears to me to be a practical advantage, that the destructive 

 caustics, if I may so term them, possess over the conservative ones. In 

 doing so I beg to state, once for all, that I offer my opinions on such points 

 with great diffidence, knowing that chemistry is not medicine or surgery, 

 but only one of their instruments. The practical advantage is this : When 

 the surgeon desires the removal of the diseased tissue by caustics, if he uses 

 a conservative caustic he kills the tissue, but has to effect its separation by 

 a further process of suppuration, etc. ; whereas, if he employs a destructive 

 caustic, the processes are in simultaneous action, and the desired result is, 

 consequently, more speedily accomplished. 



Nitrate of silver is essentially an oxidizing caustic, but its action is much 

 slower than that of chromic acid or manganese with potassa, from the cir- 

 cumstance that it does not so readily part with its oxygen; and it forms an 

 insoluble compound with organic structures, which acts as a preventative to 

 its continuous power as a caustic, by forming a sort of impermeable coating 

 on the tissue to be removed. I am aware that this action is an advantage 

 where hemorrhage is to be feared. 



The exsiccated sulphate of zinc and copper, when employed as caustics, 

 act like chloride of zinc by their powerful affinity for water. But when the 

 vis vita? is destroyed by such affinity, their further action is that of strong 

 antiseptics, thereby greatly, if not entirely, retarding the natural disruption 

 of tissues which have ceased to possess vitality. Bichloride of mercury, 

 and, in fact, all mercurial caustics, possess a conservative action, by their 

 strong affinity for the albuminous components of organic structures, with 

 which they form compounds of definite character. 



Nitric and sulphuric acids belong to the class of destructive caustics ; the 



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