xxxii INTRODUCTION

These pathogenic units Fracastorius clearly surmises to be of
the nature of colloidal systems, for if they were not viscous or
glutinous by nature, he holds, they could not be transmitted by
fomites'; while germs transmitting disease at a distance must be
able to live in the air a certain length of time,: and this condition
is only possible when the germs are gelatinous or colloidal systems;
for only hard, inert, discrete particles could endure longer.s  These
colloidal particles have the power of resisting forces of small magni—
tude, but cannot resist such agencies as extremes of heat or cold,
which reduce them to phases of dissipated energy.* Finally Fra—
castorius conceives that the germs become pathogenic through the
action of animal heat, and that in order to produce disease it is
not necessary for them to undergo dissolution, but only metabolie
change.s 'Thus Fracastorius seems to have had a clear notion (or
prevision) of the causation of disease by microorganisms, and he
appears to have seen these organisms as made up of those gelatinous
or "^dispersed" systems which modern physical chemists call colloi—
dal states of substance'.*

Contribution of Fracastorius

His theory of seminartia contagionis led Fracastorius to attack
Galen's view of the pathogeny of pestilent fevers, and to dis—
tinguish the true plague from other fevers; to give the first
accurate description of exanthematic typhus7 (lenticular fever)

: p. 14, cuius signum—conspiciuntur.

2 p. 30, non solum—servar^.

s p. 30, sed certe—possunt.

1 p. 32, non solum—franguntur.

s p. 42, quantum quidem—putrefactionem.

5 Among modern writers on the History of Medicine, who have
done justice to the originality of Fracastorius' theory of contagion,
may be mentioned: Haeser, Vol. II. p. 132, 1882; Massalongo,
1915; C. and D. Singer, 1917; A. C. Klebs, 1917; see Bibliography.
TThe lay biographers have usually neglected to mention in any
detail his contribution to medical science. The erudite and pains—
taking Mencke (1731) whose indignation at the neglect of the writ—
ings of Fracastorius led him to write his biography, though he says
that Fracastorius first had the courage to investigate prima morb—
orum et pestilentiarum semina et causas, declines to describe the
purely medical works, lest he should ^nauseate the reader'". Even
Barbarani (1897), though he devotes many pages to the poem
Syphilis, says little about CorWagion: Symonds, Sandys, Spingarn
and Saintsbury ignore it; Symonds describes the poem. Bayle,
DicfWionnaire Historique says he cannot forgive Fracastorius for
his poem on that vile distemper which he ought to have treated only
as a physician.

*Haeser, Vol. III. pp. 870 foll., under Der Petechialtyphus,
prints, without translating, Con/agion, Book II. Chh. 6 and 7, on
lenticular fever and its causes.