352 
EXPERIMENTS ON PLEURO-PNEUMONIA. 
time which we considered sufficient, but not more than suffi¬ 
cient, to afford security against previous infection. I then 
stated that we should exclude any living source of infection 
from our premises, but would “try, in succession, every 
channel of mediate contagion known to us, using in our ex¬ 
periments all that deliberation and caution which the con¬ 
sideration of the importance and difficulty of the inquiry 
enforced upon us.” 
Before proceeding with the narrative of our experiments it 
will, I think, be useful to state somewhat more fully than has 
hitherto been done, the nature of the practical questions 
which we have had in view, some of which have now assumed 
agreater importance than they had at the outset. Our objects 
have been (1) to ascertain by experiment by what different 
ways a healthy animal can be infected ; (2) to ascertain 
whether inoculation is practically useful; and (3) to discover 
a way of inoculating an animal without risk. 
With reference to the first point, the opinion generally en¬ 
tertained is, that a healthy animal may get pleuro-pneumonia 
either directly from a diseased animal, or indirectly by being 
brought into relation with its hide or carcase, or with per¬ 
sons or things that have been in contact with it body. Thus, 
Mr. Fleming, the author of the well-known Manual of Vete¬ 
rinary Sanitary Science , expressed his belief very decidedly 
in 1875, that “infection may occur through the medium of 
forage, straw, &c., which have been soiled and breathed upon 
by infected cattle, by the utensils which have been used with 
them as well as by the persons who have attended to the 
sick,” and has since that period expressed the same opinion 
in still stronger terms. An opposite view had, however, been 
guardedly promulgated by a very high authority. In the 
excellent article by Professor Brown on the contagious and 
infectious diseases of animals, which appeared in the tenth 
volume of the Journal , the author said, that “ so far as his own 
observations had enabled him to decide, the disease is only 
communicated by the actual contact of a diseased animal w 7 ith 
a healthy one, and that it is at least exceedingly probable 
that the mode of communication is by the inhalation of the 
breath of the diseased subject.” 
With reference to the second question, that of the utility 
of inoculation, opinions are also, as needs scarcely be said, 
much divided, although the majority are in its favour. One 
of the strongest arguments against it is founded on the ac¬ 
knowledged fact, that although inoculation as ordinarily 
practised produces very severe effects, yet the effects are 
neither the disease itself nor any modification of it. It has, 
