Nov. 1906. | THE PRESIDENTIAL ADDRESS. 231 
the gelatinous lumps are placed in a saccharine solution 
with some bits of ginger in a bottle, a fermentation is set 
up which results in the liquor so commonly used. Mythical 
histories attached to the origin of the gelatinous mass— 
brought from the Crimea, Italy, and so on—and the plant 
was handed on from family to family. 
In 1887 the plant came to Professor Marshall Ward, and he 
began an investigation—one which ultimately extended over 
several years. The outcome of it was that the ginger beer 
plant was shown to be composed of two essential ingredient 
plants, with several others present as accessory non-essential 
forms. Of the essential, one is a bacterium, 5. vermiforme, 
a distinet species, the gelatinous sheaths of which make 
up the jelly of the ginger beer plant. The other is a yeast, 
Saccharomyces pyriforme, also a distinct species, to which the 
alcoholic fermentation is due. Not only was this determined 
by analysis, but also by synthesis. Further, the reseach 
led to the development of a new conception in that of 
symbiotie fermentation, ie. the bacterium is favoured by 
obtaining some substance or substances directly they leave 
the sphere of metabolic activity of the yeast celis. The yeast, 
on the other hand, benefits by these substances being removed 
and destroyed, and amongst these the CO,, which seems to be 
essential for the bacterium. (A comparison with the symbiosis 
of a gelatinous lichen naturally suggests itself.) This idea of 
symbiotic as compared with metwbiotic, where one organism 
prepares only the ground for another, and antibiotic, where 
one organism ousts the other by poisoning the medium, is a 
fertile one. 
I now come to speak of an investigation the labour of 
which would have daunted most men. I refer to that of the 
bacteriology of Thames water. This he undertook for the 
Royal Society in 1892, in conjunction with Professor Perey 
Frankland. The actual bacteriological part of the work was 
taken up by Marshall Ward himself. For work of this kind 
he was well prepared, having already published his views 
upon the characters employed in the classification of Schizomy- 
cetes. It is difficult for an outsider to realise the industry, 
the constant attention, required for this bacteriological work. 
It involved the isolation and growing through all their life- 
stages in pure culture of the many forms met with in the 
