364 
ALFRED L. LOOMIS. 
life-history. They not infrequently are attached together at their 
extremities, forming zigzag chains. 
In this brief description of the principal varieties of bacteria 
(classified according to their form), we have seen that they differ 
Fig. 3,—Desmo-bacteria (Bacilli). A, Bacillus tuberculosis (x 2,000); B, the same 
(x 350); C, Bacillus anthracis, from the blood in splenic fever (x T30); D, Bacillus leprae, 
showing bacilli in cells isolated from tuberculous nodules by teasing (x 1,000). 
greatly in appearance, from the minute dot of the micrococcus 
and the elongated dot of the bacterium proper, to the elongated 
rod or cyliuder of the bacillus and the long spirals of spiro- 
bacteria. It is unfortunate that these minute forms of life are 
not sufficiently constant in habit to always attacli themselves to 
one or the other of these genera. The micrococcus has a habit of 
elongating until it is impossible to recognize him except as a 
bacterium ; while bacilli break up until their particles exactly 
resemble the micrococci. Again, there are other forms which can¬ 
not be classified with the above; but I will not at present burden 
you with the complicated forms of fungi which are found existing 
as moulds, yeast-plants, etc., but will pass to the consideration of 
the biology of bacteria. 
Bacteria cannot exist without water. Certain forms require 
oxygen, while others again thrive equally well without it; some 
thrive in solutions of simple salts, while others fastidiously 
object to anything less than broths of albuminoid material. 
