PUSTULE. 33IALL-POX. oDo 



epidermis, where it follows immediately upon the pareirjhjma- 

 toiis inflammation. A host of pus-corpuscles is generated by 

 each of the swollen cells, and the chambered dome of the pock 

 is soon filled with a yellowish purulent fluid in place of the 

 transparent lymph which it previously contained. The pus- 

 formation need not go beyond the epithelium. The pus dries 

 up, and before the pock is thrown ofl", a new epithelial covering 

 for the cutis is completed underneath it. 



As a rule however, the papillary body takes part with the 

 epithelium in the production of pus. It may do this in two 

 ways. We may distinguish between a catarrhal and a diphtheritic 

 pus-formation. For the catarrhal variety I may refer the 

 reader to § 292 and fig. 111. The suppiu'ation is superficial, 

 the papillary body remains intact, and is roofed in during con- 

 valescence by a layer of new cuticle which long continues thinner 

 than the normal epidermis. This variety of pock heals without 

 leaving any scar. Both anatomically and clinically it is a far 

 less serious affection than the ^' destructive" pock. The latter 

 consists, not in a mere secretion of pus from the papillary body, 

 but in a liquefaction of its proper substance ; hence it results in 

 loss of tissue, in ulceration and scarring. Bdrensprung has given 

 an excellent description of the naked-eye characters of the diph- 

 theritic pock, as follows : "In the second stage (of pock-forma- 

 tion) an exudation takes place wherever simple hyperaemia 

 existed ; those portions of the cutis which hitherto presented a 

 lively redness, now assume a white colour which extends to the 

 subcutaneous areolar tissue ; they seem im])regnated with a soft 

 mass of exudation ; their edges are surrounded by a red areola ; 

 the papillae too have lost their colour. In the third stage, the 

 vesicles undergo conversion into pustules. On investigating the 

 pock at this period, Ave can assure ourselves that all the infiltrated 

 part of the cutis, together with its papilla), has been destroyed 

 by suppuration. The pock exhibits a hemispherical, vaulted 

 appearance, and contains, besides pus, shreds of the necrosed 

 tissue. A fourth stage exhibits the pustules torn open at their 

 apices, and emptied of their contents ; their place is taken by 

 little open ulcers, which leave the well-known reticulated scars 

 behind them when they heal." 



The microscope furnishes us with a very simple and tho- 

 roughly explanatorv commentary on this succinct and luminous 



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