|The Different Types of Infection
The essential types of contagion are three in number:
(1) Infection by contact only.
Infection by Contact Alone
The infection which passes between fruits is markedly of this kind, e.g.,
as from one cluster of grapes to another and from one apple to another
apple.... The putrefaction that thus passes from one fruit to another
is really a dissolution of the combination innate heat and moisture by
the process of evaporation.
(2) Infection by contact and by fomites as scabies, phthisis
[tuberculosis], leprosy (elephantiasis) and their
kind. I call fomites [from the Latin, fomes
(pronounced FOH-meez) meaning "tinder"] such things as clothes,
linen, etc., which although not themselves corrupt, can nevertheless foster
the essential seeds of the contagion and thus cause infection.
(3) Finally there is another class of infection which acts not only
by contact and by fomites but can also be transmitted to a distance. Such
are the pestilential fevers, phthisis, certain ophthalmias, the exanthem
that is called variola, and their like.
The humidity (thus set free), softens and relaxes the parts and makes
them separable, and the heat effects the separation.... I regard
the particles of heat and of moisture separately, or in the case of moisture,
perhaps in combination as the essential germs of the resulting putrefaction.
I speak here of the particles of humidity in combination because
in the evaporative process of putrefaction, it often happens that the very
minute particles mingle themselves and thus generate new corruptions.
This mingling is indeed especially favorable for the propagation of putrefactions
Infection by Means of Fomites
It may be questioned whether the infection by a fomes is of the same nature
as infection that acts only by actual contact. The nature of infection
by a fomes appears, indeed, to be different since having left its original
focus and passed into a fomes it may there last for long unchanged.
It is, indeed, wonderful how the infection of phthisis or pestilential
fevers may cling to bedding clothes, wooden articles, and objects of that
kind for two or three years, as we have ourselves observed.
On the other hand those minute particles given off by a body affected
with putrefaction do not appear to preserve their virulence for long and
on that account are not to be regarded as of identical essential nature
either with those of fomites or with those that act by contact alone....
Not all substances are liable to become fomites, but only those that are
porous and more and more or less calorific, for in their recesses the seeds
of contagion can lurk hidden and unaltered either by the medium itself
or by external causes, unless these are excessive, e.g., they cannot withstand
fire. Thus, iron, stone, and cold and impervious substances of this
kind are hardly likely to act as fomites; on the other hand linen, cloth
and wood are more apt to do so.
Infection at a Distance
It is well known that the pestilential fevers, phthisis and many other
diseases are liable to seize on those who live with the infected, although
they have come into no direct contact with them. It is no small mystery
by what force the disease thus propogates itself.... For this type
of contagion appears to be of quite a different nature and to act on a
quite separate method from the others.... Thus a patient with ophthalmia
may give his disease to another by merely looking at him. This well
illustrates the rapid and almost instantaneous penetrative power of this
type of contagion ... which may be compared to the poisonous glances of
The Affinities of Infection
The affinities of infection are numerous and interesting. Thus there
are plagues of trees which do not affect beasts and others of beasts which
leave trees exempt. Again among animals there are diseases peculiar
to men, oxen, horses, and so forth. Or, if separate kinds of living
creatures are considered, there are diseases affecting children and young
people from which the aged are exempt and vice versa. Some again
only attack men, others women, and others again both sexes. There
are some men that walk unharmed amid the pestilence while others fall.
Again there are infections which have affinities for special organs.
Thus ophthalmia affects only the eye. Phthisis has no effect upon
that most delicate organ but acts especially upon the lungs. Alopeciae
and Areae confine themselves to the head.
Is Infection a Sort of Putrefaction?
We here consider whether all infection is a sort of putrefaction and also
whether putrefaction is not itself infection.... Now with Rabies
have we not infection without putrefaction? Again, when wine becomes
vinegar have we not infection without putrefaction? For, if left
to putrefy, it is later that it becomes fetid and undrinkable--the sure
signs of putrefaction--and thus differs from vinegar which is pleasant to
take and is indeed resistant to putrefaction.
But it must be remembered as regards putrefaction that sometimes there
is but a simple dissolution of the combination of humidity and innate heat
without any new generation--we then speak of it as simple
putrefaction. Sometimes on the other hand, in the process of this
dissolution, there is a true animal generation or generation of some substance
definitely organized and arranged.
When there is simple putrefaction, there is no new generation but a
[strong, horrible smell] and a horrible taste arise
... but when, on the other hand, there is neither the abominable smell
nor taste but a definite redistribution of the qualities. As with
wine ... so also with milk and with phlegm, the first stage of putrescence
is acidity. Similarly with Rabies, we must suppose a preliminary
stage in which there is a certain amount (of the same preliminary type)
of putrescence. It is, however, latent because putrefactions which
take place in the living animal do not make themselves immediately apparent.
It is an observed fact, however, that dogs which are becoming rabid are
usually seized with febrile symptoms. If, therefore, we regard the
matter inductively we shall consider that all infections may be reduced
ultimately to putrefaction.... Furthermore, all putrefactions are
liable to produce putrefactions like themselves, and, if all infection
is putrefaction, infection in the ordinary sense of the word is nothing
else than the passage of a putrefaction from one body to another either
continuous with it or separated from it.