AS PUR THER CONTRIBUTION TO THE NATURAL 
HISTORY OF BACTERIA AND THE GERM 
THEORY OF FERMENTATIVE CHANGES 
[Quarterly Journal of Microscopical Science, October 1873.] 
In April of this year I communicated to the Royal Society of Edinburgh 
some of the results of a protracted investigation into various circumstances 
connected with the appearance and growth of minute organisms in fermentable 
substances. During the time that has since elapsed I have continued to pro- 
secute the inquiry, and have obtained various new and striking confirmatory 
facts, a selection from which will form the subject of the present paper. 
In the former communication observations were related which led me to 
conclude that in some minute species of hyphomycetous fungi, the spores (conidia) 
produced upon their filamentous branches germinate in three distinct ways ; 
first, they may form comparatively thick sprouts, which become young plants, 
like the parent ; second, they may multiply by pullulation like the yeast plant, 
and under some circumstances this toruloid growth? may continue for an in- 
definite period, though the resulting progeny will, under favouring conditions, 
reproduce a fungus like the original; and, thirdly, the conidia may shoot out 
sprouts of exquisite delicacy which break up into bacteria. In accordance 
with this mode of origin of bacteria it was shown that such organisms, like 
the fungi from which they are derived, are of various totally distinct kinds, 
manifesting their differences both morphologically and still more physiologically 
by the characters of the fermentative changes to which they give rise, and by 
the circumstance that some sorts refuse to grow at all in media in which others 
thrive. Some of the species exhibited most remarkable variations in size, 
form, and movement when introduced into different media, and sometimes 
gave indications of their fungoid origin by indubitable branching, and, in the 
thicker forms, by the presence of nuclei or vacuoles. Yet, however much any 
such modification might differ from the form in which the species was seen in 
another medium, the latter variety could be reproduced at pleasure by reintro- 
duction into the habitat in which it was originally seen. 
Hence any classification of bacteria hitherto made, from that of Ehrenberg 
’ Printed at page 275 of this volume. 
* Considering the differences among authors in the use of the term torula, it seems justifiable for 
the sake of convenience to retain the old sense, as applicable to organisms like the yeast plant. 
