FOOT AND MOUTH DISEASE. 
225 
able in this fact, when it is remembered that a tuft of grass by 
the road side often holds a sufficient quantity of saliva from 
the mouth of a diseased beast to infect a herd, and the short 
period of incubation of the affection accounts for its sudden 
outbreak during a journey which occupies only a few days. 
Some of the conditions which are essential to the spread of 
the disease are known, but others of them are obscure. It 
is certain that the malady is eminently contagious and 
infectious, but it is also true that its extension in certain 
years has been apparently governed by the laws which 
regulate the spread of epidemic diseases like cholera ; and it 
has been found impossible to determine whether the 
majority of the attacks are to be attributed to the operation 
of morbific matter or virus, or to certain noncognisable 
influences, the existence of which can only be inferred from 
the effects produced. A reference to the previous observa- 
tions on the history of the disease will show that, while there 
have always been centres of infection in this kingdom, the 
malady has prevailed over a large extent of country only at 
intervals. It is not necessary to devote any time to the 
examination of the hypothesis which refers the origin of all 
contagious diseases to the presence of a ferment in the blood. 
If the idea is merely advanced as an ingenious speculation, 
it may be left to amuse those who find an interest in the 
investigation of chimeras ; but if the suggestion claims to be 
accepted as a theory, it may be refused on the ground that 
chemical and microscopic research have alike failed to demon- 
strate the presence of the germs of ferment, or the occurrence 
of any process in the circulating fluid at all resembling fer- 
mentation, either in its progress or its products. 
Examinations of the blood of diseased cattle have been 
made recently in the sheds where the sick animals were kept, 
and the highest powers of the microscope have been used in 
the investigation, but no unusual organic particles have been 
found. The fluid is in a state of excessive molecular activity ; 
the red discs are nearly all of them stellate in form, and 
change their aspect frequently, finally assuming the circular 
form. White corpuscles (Leucothytes) are more numerous 
than they are in healthy blood, and there are also seen 
many minute spherical bodies freely moving in all directions. 
Bacteria and Vibriones are constantly found; small masses 
of living germinal matter are also present ; but it is worthy 
of particular remark that all these bodies have been seen in 
the blood and other fluids of animals affected with non-con- 
tagious febrile diseases. Further, it may be accepted as a 
positive truth, that organic particles which possess the 
