ne CONTRIBUTION: TO. THE GERM THEORY OF 
PUTREFACTION AND OTHER FERMENTATIVE 
CHANGES, AND TO THE NATURAL HISTORY OF 
TORULAE AND BACTERIA" 
[Transactions of the Royal Society of Edinburgh, vol. xxvii, 1875.] 
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 infusion 
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 Cerevisiae, represented in Plate VI, 
Fig. 22 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, Penzczl- 
lium Glaucum, the commonest of all moulds, of which Fig. 1 in Plate VI repre- 
sents 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 VI, 
characterized 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 
? This communication was originally made orally to the Royal Society on the 7th of April, 1873.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 toenter upon at the time. 
I have also added facts ascertained at subsequent periods; but the dates of the observations 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 justi- 
fiable to retain for it the old name Torula Cerevisiae, a practice which has the advantage of enabling 
us to apply to similar budding cells the generic name Torula, and the adjective toruloid. 
r.-2 
