Loitping III. 
033 
multiplication within an affected animal of a particular microbe is 
intimately associated with the disease ; if, further, this microbe can 
be artificially cultivated, and with a trace of such a cultivation, or 
with the morbid matter from which it is derived, the same disease 
can, by inoculation, by ingestion, or by inhalation, be reproduced in 
a susceptible animal, with the multiplication in this experimental 
animal of the same specific microbe ; then the proof has been 
established that such disease is of the order of the infectious diseases 
and is caused essentially by that particular microbe. In the case of 
such disease the early isolation and removal, and the careful destruc- 
tion, of the affected animals is the surest means of the prevention 
and spread of the disease. Though this series of proofs is desirable 
before the problem can be said to be satisfactorily solved, it is not 
always possible to obtain it. In some of the well-known communi- 
cable diseases — e.g. small pox of sheep, small pox of man, hydro- 
phobia or rabies, and others, though these belong to the best known 
communicable diseases — the causa causans, or the specific microbe 
causing these diseases, has hitherto eluded discovery. Some of the 
ablest pathologists have in vain searched for it, yet we may take it 
as a fact that, like other infectious diseases in man and animals in 
which the search has been successful — e.g., anthrax of sheep and 
cattle, tuberculosis, swine fever, grouse disease, and a host of others 
— these diseases must be caused by living, self-multiplying microbes. 
I have therefore directed my particular attention to investi- 
gating in this direction the various diseased organs in the sheep 
affected with, or dead from, “ louping ill.” The result of this part of 
the investigation is the following : — 
1 . The blood was examined in all cases in the fresh state, and 
after the usual methods of preparation by staining, but no extra- 
neous particulate matter, and no microbes, could be detected. 
Cultivations made from the heart’s blood, and duly incubated, 
remained free from any growth. So that no microbes were to be 
detected in the blood by the known methods of examination. 
2. The examination of the cerebral fluid microscopically and 
culturally, yielded in six out of the seventeen cases positive results, 
inasmuch as under the microscope, and particularly by cultivation 
in these six cases, one and the same definite species of bacillus was 
detected. This, in specimens prepared after the usual methods of 
making coverglass specimens (drying a thin film on a thin cover- 
glass, staining and mounting this), a few short bacilli singly and in 
dumb bells could be detected ; and in cultivations made on the 
surface of nutrient gelatine and nutrient agar — by rubbing a drop 
of the cerebral fluid over the surface of these media by means of a 
sterile platinum loop — colonies came up when these were incubated 
respectively at about 20° C. (=68° F.), and at 35-37° C. (=95- 
99° F.). In two cases the number of the colonies was considerable , 
in the other four there were in each tube two or three colonies of 
this species. By saying that in six cases the cerebral fluid yielded 
colonies of one species, I ought to add that in some of these cases, 
as well as in others, from a drop of the cerebral fluid in one or the 
