504 SCOTTISH METROPOLITAN VETERINARY MEDICAL SOCIETY. 
soil will not for any length of time grow the same kind of plants, and some 
exhaust it sooner than others. 
If I am justified in asserting that zymotic diseases are due to the 
action of specific germs, possessed of vitality and special characters as 
absolute and marked as those which produce plants or animals—and 
every fact with which I am at present acquainted supports this assertion 
—then am I as justified in asserting from all the evidence before me 
that these germs cannot be spontaneously generated. Life only springs 
from preceding life—no combination of influences or conditions known 
to man will produce a plant or animal without a seed or germ—the 
causes so often invoked as operating in the production of specific dis¬ 
eases are utterly insufficient, as they can no more develop them without 
the pre-existing germ than man can be developed without pre-existing 
man. Zymotic disorders never spring up de novo. We might as well 
admit the appearance of a plant where no seed had been sown, as the 
advent of one of these disorders without a previous germ. I quite 
agree with Sir Thomas Watson when he says, that “ a disease is supposed 
to be generated de novo when the evidence is negative only, and consists 
solely in our inability to trace with the eye the continuity of a chain 
whose connecting links are known to be invisible.” To conclude from 
this that no chain exists is palpably absurd. There are a thousand 
unsuspected ways in which the invisible contagium of these maladies 
may be conveyed. 
Organic matter endowed with vitality, and composed of living particles, 
cannot be created by man, nor do we know of their independent crea¬ 
tion. The chemist or mineralogist may form crystals of organic or 
inorganic matter, but no one can create a seed, a blood-corpuscle, or a 
secreting cell. 
In adopting the argument I have done, the question may be asked, 
and has been asked, “ How did these diseases first originate if they 
cannot be developed independently now ?” Well, that question is no 
doubt pertinent enough, but it is like many more of a similar kind— 
more easily asked than answered. The answer will be forthcoming 
when we know how man, animals, and plants originated. All matter 
has had an unknown origin, and so have plants, animals, and specific 
diseases. To assert that the latter may be spontaneously developed, 
merely because we cannot explain how they first originated, is as absurd 
as to maintain that a tree or an animal may appear without the pre¬ 
existence of parent trees or animals. Assuming that these maladies are 
solely due to the presence of specific germs, and that these germs must 
exist in order to produce them, then we need not bewilder ourselves in 
. inquiring into the how and wherefore of their first production any more 
than we need do into the origin of the first man, first dog, or first 
elephant. These things are beyond our knowledge, and we can only 
deal with matters as they present themselves to us. 
Rinderpest is not a European disease, and I am not aware that any 
but writers in the public papers in 1865-66 ever said it could be de¬ 
veloped here. When little was known regarding it, we were informed 
many years ago that it was developed in Southern Russia. We now 
know that it is an Asiatic disease, and that so far from being spon¬ 
taneously generated it is always traced to a contagious source. The 
Russian veterinarians have tracked it into Central Asia, but they have 
never been able to discover where it was generated. Its existence de¬ 
pends solely upon its contagious properties, and the violation of every 
hygienic law will not produce it. When its contagium is destroyed in a 
country it will not again appear, unless a fresh supply is introduced 
