
grr das) 
XVI.—A Contribution to the Germ Theory of Putrefaction and other Fermen- 
tative Changes, and to the Natural History of Torule and Bacteria. By 
JosEPH Lister, F.R.S., Professor of Clinical Surgery in the University of 
Edinburgh. (Plates XXII.—XXVI.) 
(Read 7th April 1873.*) 
Part I. 
Although the subject of the following communication has of late years 
attracted a great deal of attention among the public generally, it may, neverthe- 
less, be well for me to preface my statements by a few elementary remarks. 
It is well known that organic substances, when left exposed under ordinary 
circumstances, undergo alterations in their qualities. For example, an infu- 
sion of malt experiences the alcoholic fermentation; a basin of paste prepared 
from wheaten flour becomes mouldy ; or, again, a piece of meat putrefies when 
so treated. The microscope shows that each of these changes is attended by 
the development of minute organisms. — In the fermenting sweet-wort the yeast 
which falls to the bottom of the containing vessel is found to consist of budding 
cells, constituting the yeast-plant, Torula Cerevisie, represented in Plate X XII. 
fig 2.t In the mouldy paste the blue crust which is the most frequent appear- 
ance, owes its colour to the spores of a species of filamentous fungus, Penzcil- 
lium Glaucum, the commonest of all moulds, of which fig. 1 in Plate XXII. 
represents a pencil of fructifying threads; and the putrid flesh will be probably 
found teeming with bodies which, in the most typical form, consist of two 
little rods, connected endways as by a joint, such as are seen at a, fig. 3, Plate 
XXII., characterised by astonishing powers of locomotion, and, from their rod- 
like form, termed Bacteria. 
The Germ Theory supposes that the organisms are the causes of the changes ; 
that the germs of these minute living things, diffusible in proportion to their 
minuteness, are omnipresent in the world around us, and are sure to gain access 
to any exposed organic substance ; and, having thus reached it, develope if it 
prove a favourable nidus, and by their growth determine the chemical changes ; 
and further, that these organisms, minute though they appear to us, form no 
* This communication was originally made orally to the Royal Society on the 7th of April 1873. 
In preparing it for the press I have introduced various details which I was unable to enter upon at 
the time. I have also added facts ascertained at subsequent periods; but the dates of the observa- 
tions being always mentioned, there will be no difficulty in distinguishing between those made before 
and after the delivery of the original address. 
+ In the present state of uncertainty regarding the true affinities of the yeast-plant, it seems 
justifiable to retain for it the old name Torula Cerevisice, a practice which has the advantage of enabling 
us to apply to similar budding cells the generic name Torula, and the adjective toruloid. 
VOL. XXVII. PART III. 4N 
