organic bases may
sometimes be formed, and may be toxic, the important toxins are not of that
nature. A later research by Brieger along with Fraenkel pointed to the
extracellular toxins of diphtheria, tetanus and other diseases being of
proteid nature, and various other observers have arrived at a like
conclusion. The general result of such research has been to show that the
toxic bodies are, like proteids, precipitable by alcohol and various salts;
they are soluble in water, are somewhat easily dialysable, and are
relatively unstable both to light and heat. Attempts to get a pure toxin by
repeated precipitation and solution have resulted in the production of a
whitish amorphous powder with highly toxic properties. Such a powder gives
a proteid reaction, and is no doubt largely composed of albumoses, hence
the name _toxalbumoses_ has been applied. The question has, however, been
raised whether the toxin is really itself a proteid, or whether it is not
merely carried down with the precipitate. Brieger and Boer, by
precipitation with certain salts, notably of zinc, obtained a body which
was toxic but gave no reaction of any form of proteid. There is of course
the possibility in this case that the toxin was a proteid, but was in so
small amount that it escaped detection. These facts show the great
difficulty of the problem, which is probably insoluble by present methods
of analysis; the only test, in fact, for the existence of a toxin is its
physiological effect. It may also be mentioned that many toxins have now
been obtained by growing the particular organism in a proteid-free medium,
a fact which shows that if the toxin is a proteid it may be formed
synthetically by the bacterium as well as by modification of proteid
already present. With regard to the nature of intracellular toxins, there
is even greater difficulty in the investigation and still less is known.
Many of them, probably also of proteid nature, are much more resistant to
heat; thus the intracellular toxins of the tubercle bacillus retain certain
of their effects even after exposure to 100deg C. Like the extracellular
toxins they may be of remarkable potency; for example, fever is produced in
the human subject by the injection into the blood of an extremely minute
quantity of dead typhoid bacilli.

[Sidenote: Enzymes.]

We cannot as yet speak definitely with regard to the part played by enzymes
in these toxic processes. Certain toxins resemble enzymes as reg