PUCCINIA FAVI. 233 



S 

 traction, when the latter does not run exactly in a vertical 



direction. The stalk varies most in size (from 0*00015 0-00030 

 mm.) and in diameter (from 0-00032 0-00160 mm.) ; it always 

 appears quite flat, sometimes round at the end, sometimes broad 

 and blunt ; and, in that case, generally very short, often twisted, 

 or ending towards its lower end in two hooks. It is sometimes 

 found without a stalk, which was probably torn off. Robin 

 observed four abnormal articulations in Puccinia. The latter is 

 always very soft, especially its stalk, which rolls itself up from 

 one side to another when it is long. 



This parasite is more likely to be met with in the small fine 

 white scales at the commencing formation of the crust below, 

 than on the large yellow favus-scales. This is, however, not 

 always the case. The place which the Puccinia occupies is not 

 always easily determined^ and it is doubtful whether it thrives 

 best on the outer or inner surface of the scale, or what 

 appears to be most probable in its midst. The whole plant is 

 0-00200 348 mm. long, the body alone 0-00415 188 mm., 

 and the stalk 0-00032 0*00160 mm., whilst the body alone is 

 0-00056 70 mm. broad, and the stalk O'OOOIS 30 mm., the 

 cellular tissue being 0-00008 10 thick. It cannot be denied 

 that this parasite belongs to Corda's Puccinia, according to the 

 above description. Among the fifty species separated by almost 

 imperceptible distinctions, it stands nearest to Puccinia Alliorum, 

 P. Virga-aurea, P. Polygonorum, especially to the last mentioned, 

 differing from it only in a few points, on account of which 

 Ardsten places our fungus in a separate species, which he calls 

 Puccinia Favi, because it is principally met with on crusts of favi, 

 although not exclusively, since it also occurs in other diseases of the 

 skin, for example on the fine scales in pityriasis. The Puccinia, 

 which was first pointed out to Ardsten by Boeck, of Christiania, 

 occurs very frequently, if not always, in cases of favi. It is often 

 very difficult to discover, and a single scale may often be examined 

 for hours and no Puccinia discovered. Cazenave, who has not 

 yet been brought to acknowledge the vegetable nature of the 

 favus, regards Puccinia as merely an abnormal product of secre- 

 tion. Robin thoroughly refuted Cazenave's view, and we cannot 

 do better than quote his final sentences : 



1. Achorion Schoenleinii deteriorates the skin, and causes 

 disease by its incessant accumulation and increase. 



2. Puccinia is merely an accessory epiphenomenon, often 



