De. Buchanan mi the Fibrin contained in tfi£ Animal Fluids. 133 



rV. — BLISTEB LIQUID. 



1. Mode in which Blisters are produced. — It is well-known that 

 when a cantharides plaster, or other local irritant is applied to the 

 skin, the epidermis is detached from the corium, and raised in a 

 blister. This detachment implies, that the fluid contained in the 

 blister has been poured out with so much force from the surface of 

 the corium, as to rupture all the organic connections between the 

 corium and epidermis. There are no vascular connections between 

 these tissues, but the epidermis is bound down by the ducts of the 

 sudoriparous glands and sebaceous follicles, which must of course be 

 ruptured whenever a blister rises on the skin. The epidermis is also 

 bound down by the hairs, which constitute a much firmer bond of 

 connection, and accordingly, the irritation and other circumstances 

 being the same, it is the number of hairs arising from the surface that 

 determines the size of the blister produced. Hence it is, that bhsters 

 upon the head are generally said not to rise, the minute vesications 

 produced occupying only the interstices between the hairs, and not 

 attaining the largo size which they often have upon the breast, sides, 

 and other parts less provided with hairs. 



2. Sources of Liquid. — Whence does the liquid of blisters proceed ? 

 As it is formed instantaneously in cases of scalding, it might be sup- 

 posed to proceed from ruptured vessels, but there is no reason to 

 think that any vessels are ruptured in the process of vesication. The 

 liquid proceeds, in all likelihood, almost entirely from the capillary 

 vessels which are ramified so plentifully on the surface of the skin, 

 and which, when they are distended with blood in inflammation, pro- 

 duce similar vesications. Nevertheless, as the liquid of blisters is not 

 quite identical with the serum of the blood, it is not improbable that 

 a small portion of it may proceed from the large lymphatic vessels on 

 the surface, and from tho ruptured ducts of the sudoriparous and 

 sebaceous glands. 



3. Qualities o/, and changes which it undergoes.— Hho phenomena 

 exhibited by the blister liquid at different periods after effusion, has 

 not, so far as I know, attracted the attention of physiologists. The 

 liquid portion of it has been frequently subjected to chemical analysis, 

 but of the more interesting coagulable portion no notice has been 

 taken. When the blister liquid is drawn off, soon after being effused, 

 it yields a coagulum so small, that it may readily escape observation ; 

 when it is not drawn off till later, the coagulum becomes more 

 abundant, and generally tho more advanced the period of drawing it 

 off, the more abundant is the coagulum. I once drew off, in a case of 

 burn, about 4 oz. of serum from some large vesications several days 

 old. The serum was perfectly liquid as it flowed into the cup in 

 which I received it ; and also some time afterwards, when I transferred 

 it from the cup into a bottle : but on examining it soon thereafter, it 



