INFECTIVE AND CONTAGIOUS DISEASES. 
21 
certain the contagious power resides in certain lesions ; and it is a 
reasonable hypothesis that the contagium is an organism with 
definite life conditions; hence we may hope to see the organism, 
to grow crops of it, and thus from distant generations reproduce 
the same disorder ; to trace its transit through the body from 
the seat of inoculation, to discover what relations exist between 
the specific lesions and the bacterium. But we may reasonably 
suppose there are some Bacteria too small to be seen by our 
present artificial aids to vision. Klebs introduced the “fractional 
culture method j” which, however, has only a limited value, as so 
many conditions are necessary to its success. The secondary repro¬ 
duction of disease in the higher animals is important, but more 
precaution than is generally adopted must be taken to prevent 
the accidental communication of the disease under investigation 
to the experimental subjects by contagion. The culture method, 
unguided by sight, is very difficult. Error is liable to arise from 
confusion of harmless Bacteria with the virulent forms. 
Lecture II.—Specific contagious disorders may possibly be 
due to the introduction of lowly organisms into the system, or, 
according to some, of altered protoplasm which is capable of com¬ 
municating to other protoplasmic masses, similar changes to those 
which it has itself undergone. Most infective diseases are pro¬ 
ducible by animal fluids at certain stages of decomposition, and it 
is held that Bacteria are either the essential contagia or that 
they generate the poison which originates the infective process. 
Some, however, consider they are simply innocent parasites, and 
so to prove that these organisms are contagia, they must be iso¬ 
lated, cultivated, and when introduced by inoculation into the 
system of an animal, reproduce the disease. With some forms 
this is very difficult, so we often need to base our conclusions 
with regard to some special organism and its resulting disease 
on analogy. The poisonous material sepsin, which is produced 
by the action of Bacteria concerns only a small number of cases 
of septicaemia as they occur clinically, this is not a virus but a 
poison, its presence is a matter of importance, but it does not give 
a clue to those cases where only an extremely minute quantity of 
material introduced causes death, the fluids of the subject of the 
experiment being active when used for inoculation. The par¬ 
ticular stage of decomposition is important, as generation of the 
septicaemia-producing material occurs only during the early stages, 
and may be lost at other stages, as was observed by Davaine long 
ago. With regard to the power of different forms of Bacteria to 
cause septic poisoning, it is presumed they constitute the essen¬ 
tial virus, for it is known that many Bacteria are reproduced 
in the body, and that fluids devoid of Bacteria have no powers 
