350 
THOMAS WALLET. 
SHEEP DISEASES: THEIR CAUSES, NATURE AND PREVENTION.* 
By Thomas Wallet, M.R.C.V.S. 
(Continued from page 322.) 
In addition to blood diseases proper we have also to notice 
those due to parasites: 
Disease-producing (pathogenic) parasites form two classes, 
viz., vegetable and animal parasites. 
Vegetable parasites are again subdivided into two important 
classes—(1) Mould fungi (hyphomycetes and blastomycetes); 
(2 ) fission or cleft fungi (schizomycetes); and in reference to 
these fungi the remarkable fact may be noticed that they are 
identical in form (morphologically) with the fungi by whose 
agency the various processes of decomposition of organic matter 
in the soil are carried on ; the former class requiring a liberal 
supply of oxygen, are found on the surface, the latter in the 
deeper strata of the soil. 
Those fungi which are engaged in such beneficent processes 
as the breaking up of organic matters for the use of vegetables 
are, so far as we know, innocent in character, or non-pathogenic ; 
but grave doubts have been entertained by many as to their 
innocency under all circumstances; indeed, some pathologists 
insist that innocent organisms do sometimes contract destruc¬ 
tive properties and it would be difficult to prove otherwise; if 
there is any truth in the theory of evolution as applied to the 
higher, there is no reason why the theory should not apply equally 
to the lower organisms. 
The ordinary eruptive diseases are aphtha, ecezema of the lips, 
and so-called carbuncle of the lip and the coronets. 
Of aphtha or thrush we have two forms, viz., a benign and a 
malignant—the former attacking lambs usually, the latter also 
being seen in ewes, and when so occurring being propagated 
from the ewes to the lambs by the medium of the milk. 
Mild aphtha is attributed to a fungus designated the “ oidium 
albicans.” The malignant form is also probably due to a fungus. 
♦Transactions of the Highland and Agricultural Society of Scotland. 
