31 
suppurations. As to the part which’ bacteria play in the causation 
of these diseases, Dr. B. Sanderson says : ‘‘The presence 0 
characteristic organic forms in infective liquids affords in itself no 
conclusive evidence that these bodies are themselves the cause 
of the infectiveness. If we inferred from the constancy of their 
characteristics and from their invariable presence that they are the 
agents which produce the pathological results, we might be as 
seriously in error as those who maintain, in the face of all the 
investigations made during the last few years, that they are without 
pathological significance. There is nothing in nature, and par- 
ticularly in organic nature, without significance ; nor ought it to 
diminish the interest which we take in any phenomenon, that we 
are unacquainted with its relation to the other phenomena with 
which we find it associated. If these infinitely mimute organisms 
are present in every intensely infective inflammation, we may be 
quite sure that they stand in important relation to the morbid 
process.” 
Not only in acute infective inflammation, but also in diphtheria 
and erysipelas, microzymes, such as we find associated with 
ordinary putrefactive processes, have been discovered. 
Beyond the discovery of the relation which microzymes (such 
as excite ordinary putrefaction), hold to what may be called 
the common process of disease, e.g., infective inflammations, diph- 
theria, and erysipelas, our knowledge has advanced so as to enable 
us to connect certain specific diseases with specific organic vegetable 
forms. A large number of diseases have one character in common. 
They are capable of being communicated from one animal to 
another, either of the same or some other species. They are 
popularly spoken of as ‘‘ catching,” and scientifically, as infectious 
‘or contagious (communicable would be a better word), as in all 
such diseases the infecting agent or contagium consists of particles 
of extreme minuteness, with respect to which it can be asserted 
that the material of which it is composed is (1) not soluble in 
animal liquids, (2) is not volatile at ordinary temperatures, (3) that 
it possesses a specific gravity very slightly different from the liquid 
in which the particles are suspended. 
The fever and other morbid processes which ensue at a short 
interval of time after the entrance of the germs into the system, 
are (probably) closely connected with their growth and multipli- 
cation. The smallest amount of contagium capable of exciting 
disease has an almost indefinite power of multiplication in the 
body. 
T have already said that a connection has been traced between 
certain diseases and specific vegetable forms. These forms of 
vegetation have been found to be present in the contagious liquids ; 
