Bacteria , their Nature and Function. 
869 
stances at the expense of relatively simple nitrogenous bodies, such 
as ammonium tartrate, urea and allied substances, or which can do 
this even by the absorption of free nitrogen of the air. Other 
species require for their growth and multiplication nitrogenous sub- 
stances as complex as the animal body itself, and, like this latter, are 
capable of breaking them up into simpler combinations. Patho- 
genic ( i.e . disease-producing) bacteria and many of the species 
concerned in the decomposition and putrefaction of albuminous 
substances belong to this group. 
All bacteria multiply by division ; hence their name, Schizo- 
mycetes, or fission fungi, the typical process of multiplication con- 
sisting in the enlargement of an individual, and its subsequent 
splitting into two by fission, at the conclusion of which process two 
new individuals are the result, each of them capable of enlarging 
and again dividing in the same way into two, and so on. But it 
can be easily shown by comparative observations, and examination 
of suitably prepared specimens of artificial cultures of the different 
species, that not seldom the process of multiplication does not 
follow this line. 
I was able to show at this stage a lantern slide of a microscopic 
specimen of one of those species which, owing to the spherical or 
nearly spherical form of the elements, is called a Coccus, or Micro- 
coccus ; and, owing to the manner of growth in clusters and con- 
tinuous masses, is called a Staphylococcus ; this microscopic speci- 
men was obtained by the method of making “ impression prepara- 
tions ” ; that is to say, by means of a thin glass pressed on to a 
recent, i.e. a young colony or colonies growing on the surface of a 
solid medium, an exact impression is obtained of the growth, and a 
good and correct insight is obtained into the manner in which the 
colony enlarges, and the way in which the individuals constituting 
the colony grow and multiply. This photographic representation 
shows that there are a good many individuals many times (4-10 
times) as large as others, that some of these large elements are 
uniform, while others show just the indication of a transverse 
fissure by which the large element is dividing ; still others show 
two fissures at right angles, by which the big element becomes 
divided into four smaller ones. But it is seen also that the majority 
of the cocci are only minute dots, some in pairs, others in clusters, 
the former looking like two demi-lunes separated by a straight 
clear line ; in fact, this latter appearance denotes the typical man- 
ner in which one coccus, having first enlarged a little, divides into 
two small elements. But the presence of the huge elements men- 
tioned above tells us also that one coccus may go on growing to a 
very large size without dividing, and, having reached this huge dia- 
meter, then commences to divide, first into two, then into four, 
eight, and sixteen individuals of the typical size. 
A second specimen shown was an impression preparation of a 
recent colony of another species ( Bacillus coli), the individuals of 
which are rod-shaped or cylindrical, and are what are called typical 
bacilli. Here the great majority of the individuals are of cylindrical 
