PAPULE. — WHEAL. 341 



Most papules are redder than the surrounding skin ; this is no 

 more than might be expected, since the formation of a papule 

 is preceded by a concentration of the hyperaemia at the affected 

 point ; the occurrence of exudation however, tends to check the 

 hypertemia by taking up the available space, and so squeezing 

 out the blood — the only constituent of the papilla which is 

 free to escape. Thus it may happen that the papules are not 

 redder than the surrounding surfiice, but of the same colour, 

 or even paler. 



Papular eruptions are most common in connexion with 

 measles. 



§ 290. — o. The wheal stands in close anatomical relation- 

 ship to the papule. Wheals {pomphi) are broad and flat 

 elevations of the skin, firm to the touch, as may readily be 

 perceived by passing the hand lightly over them. The 

 smaller wheals, those no bigger than a lentil, are circular ; 

 larger ones, often of very great size, are produced by the 

 confluence of the smaller ones and accordingly exhibit the 

 utmost irregularity of outline. The smaller wheals are of 

 the same colour as the surrounding skin ; they are seldom 

 redder. The larger however and especially the more raised 

 the wheal is, the more does its redness appear to be pushed 

 to one side and concentrated in a narrow band along its edge, 

 while its central part grows more and more pale. Finally 

 vfc may have white wheals with a red areola. These may be 

 regarded as the highest stage in the development of the 

 lu'tical exanthem. 



The wheal is an acute inflammatory oedema of the papillary 

 body. The exudation is thinner and more serous than in the 

 case of the papule ; hence too, the rash is so very fleeting, that 

 it may readily be increased by scratching, while it quickly fades 

 without any trace, if left to itself. The seat of the infiltration 

 has been already indicated. In the higher degrees of pomphosis 

 the papillary body is swollen to such an extent that the flow of 

 blood through it is completely arrested ; the blood which is 

 meant to supply the part is retained at its periphery, where 

 it accumulates. The red areola of the white pomphus is there- 

 fore due to collateral hyperasmia resulting from the imperme- 

 ability of the capillary networks in the interior of the swollen 

 region. 



