LIFE-HISTORY OF PENICILLIUM, 843 
the cheese, the bread, fresh and preserved fruits, and many 
ways have been tried to destroy it or keep it under. It alone 
is the cause of many of our domestic arrangements, and 
much care must be taken during expeditions to prevent 
bread, flour, and other substances becoming mouldy. It is 
often content with the poorest food, which would be too 
bad for higher fungi. It lives in the human ear; it does 
not shun cast-off clothes, damp boots, or dried-up ink. 
Sometimes it contents itself with a solution of sugar with 
very little inorganic matter, at other times it appears as if it 
preferred the purest solution of a salt with only a trace of 
organic matter. It will even tolerate the hurtful influence 
of poisonous solutions of sulphate of copper and arsenious 
acid. No wonder that, as this fungus is so well fitted to be 
everywhere victorious in the “struggle for existence,” it 
soon overcomes all other forms that come in its way. In 
the natural course of a spontaneous or artificial cultivation 
of mould the same tragedy is surely repeated. At first 
appear the statelier kinds of mould, the long-stemmed 
Mucorini and their allies, which fruit only on account of 
their more rapid growth. Among them Penicillium appears 
in three or four days; at first harmless and modest, in the 
form of delicate white specks of mycelium. These grow 
with fabulous rapidity in all directions, and form large patches 
spreading out and covering the whole substratum. But even 
before this takes place there are, as a rule, noticeable in 
the middle of each tuft, not higher than half a line from the 
substratum, small, alabaster-white, thick tufts, which are 
the conidia-bearing aerial hyphe of Penicillium. From the 
centre of the cluster, and therefore from the centre of the 
whole group, begins a change from white into blue, which 
indicates the ripening of the spores. ‘The blue colour spreads 
centrifugally over the whole patch, leaving only a white edge. 
At length even the edges becomes blue, and in from seven 
to ten days the whole substratum is covered with a blue 
coating, which, on the slightest agitation, gives off clouds of 
spores. When the whole substratum is exhausted the cul- 
ture of the Penicillium ends. Other fungi have no chance 
of growing during the period of vegetation of the Peni- 
cillium, and any subsequent development in the exhausted 
nutrient substance is impossible. Penicillium is the plebeian 
despot among the moulds—mould par ezeellence, and the 
form meant when we use the word mould. 
Penicillium was undoubtedly long familiarly known before 
it received any scientific notice, as its minute size would 
prevent its examination until sufficiently high magnifying 
