Ape., 1889. 
PRESIDENT S ADDRESS. 
75 
latest born of the sciences—I mean that which bears the 
somewhat cumbrous title of Bacteriology. Our attention 
will be confined mainly to certain questions of their physio¬ 
logy and modes of occurrence, upon which now our 
knowledge is more exact than it was some years ago. 
Bacteria (more properly called Schizomycetesj are minute 
cells devoid of nuclei, which are able to derive their nitrogen 
from ammonia compounds, and are therefore not animal but 
vegetable cells. They are also devoid of chlorophyll, and 
therefore belong to tli'e group called Fungi. A great part of 
their substance consists of water, even as much as eighty- 
three per cent. Of the dried constituents we find— 
A nitrogenous substance 
... 84-20 
Fatty matter ... 
... 6-04 
Ash (mineral)... 
... 4-72 
Undetermined 
... 5-04 
100-00 
The only one of these which calls for particular descrip¬ 
tion is the nitrogenous substance, which is analogous to the 
protein of other members of the vegetable kingdom, and is 
therefore called::Mycoprotein. It forms the essential constitu¬ 
ent of the protoplasm ; it varies slightly in different species, 
but so far as is known at present contains no sulphur or 
phosphorus. The cell-wall usually consists of cellulose, but 
according to Nencki the cell-wall of the putrefactive Bacteria 
consists of a mixture of cellulose and mycoprotein. It is 
certain at any rate that the wall of the latter is acted upon 
by various staining agents which also act similarly upon the 
cell-contents, while in the case of the other Bacteria the cell- 
wall and the cell-contents are differently affected. Vincenzi 
states that the cell-walls of Bacillus subtilis contain no 
cellulose, and thus they approach the character of the cells 
of animals. 
The cell-contents are protoplasm (chiefly consisting of 
mycoprotein) and various inorganic substances in minute 
proportions, such as the salts of potash, lime, soda, magnesia, 
or iron. A few species contain starch granules, and are 
coloured blue by iodine; others contain pure sulphur in the 
form of non-crystalline granules. The colouring matter of 
most coloured Bacteria is external to the cell, being of the 
nature of an excretion ; but in a group, of which Beggiatoa 
( Clathrocystis ) roseo-persicina is the type, it exists dissolved 
in the protoplasm, and is of a peculiar nature. The ordinary 
pigments of Bacteria can only be developed by the aid of free 
