Bacteria, their Nature and Function. 
371 
which was next shown, growing on nutritive gelatine, is made up of 
twisted and convoluted threads of cylindrical rods, which threads 
are seen to shoot out and to extend like filaments from the margin 
of the colony. Instead, however, of these filaments being made up 
of the typical cylindrical rods, the former consist of relatively huge 
spindle-shaped or spherical masses many times the diameter of the 
typical rods. The threads of this colony are perfectly active, and 
are growing with vigour and in perfectly normal circumstances as 
regards soil, temperature, and all other known conditions. As a 
matter of fact, a few days later, as comparative specimens show, all 
threads may be, and as a rule are, again of the typical aspect, i.e. 
uniform threads and chains of rod-shaped elements. 
Another photograph shown was from a colony of the bacillus of 
diphtheria. Here also we notice the appearances already mentioned 
of the anthrax bacilli, viz. shorter or longer filaments, in which 
some of the elements show a conspicuous enlargement ; pear-shaped, 
spherical, or club-shaped. Such forms are not involution forms : 
they occur in vigorous and actively growing young colonies. 
A still further illustration, and one of great importance, was 
shown by a photograph illustrating a similar change of the tubercle 
bacilli. This change has now been confirmed by several indepen- 
dent observers. The typical tubercle bacilli of human or bovine 
tubercle and of early cultivations are cylindrical rods. In cultiva- 
tions of long duration but still actively growing we notice forms 
which are more filamentous, and, as in the present illustrations, are 
branched filaments with club-shaped enlargements. 
From all this the conclusion is justified that in all these cases of 
bacilli the typical cylindrical bacilli show occasionally an indication 
that reminds one of forms belonging to the higher or mycelial fungi, 
in which the growing filaments remain unsegmented and become 
thickened and even branched. These thickened, branched, and 
club-shaped forms of the bacilli would correspond to an atavism, and 
would recall a probable former fungoid phase in the evolutional 
history of these bacilli. 
The next point to which I wish to direct attention is the rapidity 
with which multiplication of the bacteria takes place. This differs 
according to the amount and nature of the nutriment or soil on 
which they grow, and to the temperature. While some bacteria 
multiply even at lower temperatures at a great rate, others do so 
only at higher temperatures. But in order to convey an idea of the 
power and the rate of multiplication I may mention the following : 
Direct observations show that the rate at which bacteria divide at 
a temperature of 64° F. varies from eighteen minutes to thirty 
minutes or a little longer, and at higher temperatures correspond- 
ingly faster. A tube of nutrient broth was inoculated with a trace 
of the growth of a staphylococcus ( Staphylococcus pyogenes aureus), 
the number of cocci introduced into the tube having been previously 
determined to be 8 per cubic centimetre. The tube was then kept 
at 99° F. ; in the first twenty-four hours the cocci had multiplied 
to 640,000 per cubic centimetre ; in the second twenty-four hours 
