GERM-THEORY OF DISEASE. 345 
internal parasites, he had no hesitation in accusing as the cause of 
the disease. 
The actual proof of this, by separating the organism, cultivating 
it free from anything to which the disease might be aseribed, and 
subsequently producing the disease in a healthy animal by innocula- 
tion of such pure cultures, was delayed for many years. Neverthe- 
less, Dayaine’s was an epoch-making discovery, and the insight which 
has been gained into the relationships between microscopic organisms 
and disease is very largely owing the classical researches of Pasteur, 
Koch and others on Anthrax. To these and similar researches 
biology is much indebted fer additions to the knowledge of the group 
of Fungi to which these disease-producing organisms belong, and 
enquiries into the natural history of the group as a whole have been 
thereby stimulated, which have led to many interesting results. 
The present paper is intended to indicate a few of the most import- 
ant of these. 
Although the function of the green-colouring matter of plants 
cannot yet be regarded as definitely established, coloured forms are 
nevertheless known to be able to draw their carbon from the 
carbonic acid of the medium in which they live, while colourless 
forms depend on living or dead organic matter for their food, and 
are thus either parasites or saprophytes. Most of the colourless. 
plants belong to the lowest vegetable sub-kingdom (the Thallophytes), 
and constitute the class Fungi of that subdivision. Coloured and 
colourless Thallophytes exhibit various grades of organization, but 
with the exception of the Mould-Fungi all of the organisms which 
produce disease belong to the lowest grade, which reproduce them- 
selves mainly by division or fission, and have on this account 
received the ordinal name of Schizophytes. 
Among the Mould-Fungi both parasitic and saprophytic forms are 
to be found. Many diseases of plants are attributable to the 
former, and not a few of thuse incident to the surface of the body in 
animals. Under ordinary circumstances the interior of the body is 
not favourable to the development of moulds: not only is the 
temperature too high, but the alkaline reaction of the fluids and the 
scarcity of oxygen are both factors which hinder their growth. It 
is otherwise with the colourless Schizophytes ; the conditions which 
1 Recent researches appear to indicate that Chlorophyll protects the lirst products of 
assimilation against the decomposing action of light. 
