Louping 111. 
629 
And the question is, “ What causes this congestion ? ” or, in other 
words, “ What is the causa causans 1 ” 
Etiology. — The consideration of this question brings us to the dis- 
cussion of the etiology of the disease. There are, in the first place, 
several points which are well established, and which, by themselves, 
strongly point to the malady belonging to the class of infectious 
diseases. 
1. The disease has a seasonal and local epidemic character. As 
is well known, cases of “louping ill” commence during the second 
half of April ; they steadily increase in number towards the middle 
of May, and then decrease again, so that, by the commencement of 
June, the disease vanishes for the year. In this respect its similarity 
to the epidemic and seasonal character of some infectious diseases 
in man and animals — e.g. cholera and grouse disease — is obvious and 
striking. As is well known, epidemics of the above diseases com- 
mence at a particular season ; cases, at first few, gradually increase 
in number till the climax is reached, and then as gradually diminish 
so as to again almost completely disappear. With regard also to 
preference for one locality to another, the “ louping ill ” partakes of 
the character of infectious diseases. It is well known that this 
disease is present only in particular districts in Northumberland 
and Scotland, is absent from others, and is, as far as I can learn, 
not known south of Northumberland. Even in districts where the 
disease prevails, a fence between one sheep farm and the next is, I 
am informed by experienced farmers, occasionally found to be the 
boundary between an infected and non- infected area. This same 
fundamentally important local predilection forms a conspicuous 
feature in some infectious diseases, both of man and of animals — e.g. 
cholera. 
2. The causa causans of the disease is contained on, or in, the 
soil. In illustration of this there is the well-established fact that if 
from any farm in which the disease had occurred the animals are 
removed and a new flock from a non- infected locality brought into 
the farm, the disease at the proper season will make its appearance 
amongst the new flock, and, as a rule, to a greater extent than 
before. The infectious diseases to which similar characters belong 
are not rare ; thus, in anthrax or splenic apoplexy of sheep and 
cattle, the actual mode in which the animals contract the infection 
is by receiving the contagium of anthrax from the soil, in and on 
which it is diffused, and from which, by the respiratory or digestive 
organs, it is received into the animal. In malarial fever of man 
(ague) the contagium of the disease lives and thrives in marshy soil, 
and from here finds its entrance into the respiratory organs and the 
blood by the instrumentality of the air. 
Now, with regard to “ louping ill,” I learned that it is the 
almost universal custom that, when an animal dies, its carcass is left 
on the moors and there rots away till it disappears. Supposing that, 
as in infectious diseases, the body of an animal that has succumbed 
to the disease contains the contagium in an enormous crop of the 
specific microbes, it is obvious that if such an animal is allowed to 
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