Hogg, on Vegetable Parasites. 
17 
looked upon as an example of the conversion of an animal into 
a vegetable product. It is quite possible, without a careful 
microscopical examination, to mistake the stroma, always 
present in large quantities in favus crusts, for pus. This, I 
think, is a mistake often committed by the more casual ob- 
server. We will not, however, enter into any discussion 
upon this theory, nor upon one still more improbable, " the 
spontaneous generation hypothesis^^ — of all hypotheses the 
most gratuitous ; I was almost about to say absurd. 
I must now be permitted to add a few words upon the 
physical aspect of persons suffering from favus, hQCdiw^e, as 
I have already stated, and not without proof, that such diseases 
are the embodiment, or rather the impersonification, of a 
weakly, unhealthy state of the body, well understood as 
the scrofulous habit; and associated with a dirty or neg- 
lected state of the skin in the majority of cases. Hebra, the 
great authority on skin diseases, lays much stress upon the 
feature of dirtiness as a cause of favus, and goes so far as to 
say that this accounts for its rarity among the upper classes 
of society. The subject of one of the worst cases,''^ says 
Mr. Hunt, " was a puny, half- starved boy of seventeen, whose 
appearance was that of a child of nine or ten. When he was 
taken from his miserable home into purer air, and well fed, 
the crusts died and dropped off ; but when he returned to 
the wretched habitation of his parents, situated in one of the 
filthiest parts of Lambeth, and was insufficiently fed, the ve- 
getation grew again most rapidly — ^flourishing in the vitiated 
fluids like a vine in a mass of stercoraceous mould .''^ From 
this boy I obtained, in 1859, large supplies of the fungous 
crusts, and at that time, to make sure of the results of my exa- 
minations, I sent portions of the same to friends upon whose 
experiments I could rely for the confirmation of my own. 
Having perfectly satisfied myself, and not by one but by 
many trials, that the achorion (favus) produces as good a 
ferment, and nearly as briskly, as healthy yeast, when added 
to barley -wort, with only a slight difference of size and form 
a difference of degree, and not of kind,^^ my next experi- 
ment was one slightly varied, for the purpose of observing 
the modifying influence of light over these fermentations, 
and at the same time ascertaining if this agent at all affected 
the character of the results. I was, perhaps, led to make this 
observation from finding that yeast requires for its more per- 
fect growth, not only a proper temperature, but almost occlu- 
sion from daylight — a fact that appears to hold good in the 
development and growth of most fungi. I therefore, in April 
last, procured a supply of fresh wort from a brewery, which 
VOL. XIV. b 
