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 ascribed, and 

 subsequently producing the disease in a healthy animal by innocula- 

 tion of such pure cultures, was delayed for many years. Neverthe- 

 less, Davaine's was an epoeh-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 for 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, 1 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 those 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 first products of 

 assimilation against the decomposing action of light. 



