THE BACTERIACEZ. 189 
peded by a mucilage, they often swim very vigorously. They are 
sometimes found felted together in a motionless mass. 
When the bacteria in any fluid have absorbed all the nutriment 
it contains, they fall to the bottom and form a precipitate; but, 
according to Cohn, they are not dead, and if a fresh supply of 
pabulum be added, they will rise and multiply. 
The extreme minuteness of the smaller forms of the Bacteriacez, 
such as Micrococcus, especially those which do not exhibit move- 
ment, renders them very liable to be confounded with other 
particles, organic and inorganic débris of various kinds. Inorganic 
substances may be distinguished by their angular form, their inferior 
capacity for refracting light, their chemical reactions, and their 
molecular or Brownian movement. ‘The discrimination of organic 
substances, which Cohn calls “ pseudobacteria,” is more difficult. 
Their form, however, is not so regular, their refractive power is 
less, and their colour variable, In doubtful cases, Tiegel re- 
commends the slide to be warmed, when bacteria will exhibit 
characteristic motion, z.¢., in a straight or curved line, not molecular. 
Dr. A. Magnin gives the following arrangement of signs, after 
Hiller, for diagnosing bacteria : 
A. The optical signs. 
1. The characteristic vegetable form, rods, /epfothrix, &c. 2. 
The characteristic movements of the monads. 3. The mode of 
growth and multiplication. 4. The mode of junction of the 
granules. 
B. Zhe chemical signs. 
1. False zooglea become softened and diffluent under the action 
of liq. potassze, and are coagulated by the direct application of 
alcohol. 
2. In sections of tissues, after an hour of maceration in liq. 
potassze, diluted ;4,th, the monads are coloured brown by iodine, 
while fat granules are not. 
In the coagulation of milk, minute globules of caseine are 
formed, which exhibit molecular motion. They are soluble in liq. 
potassze, whereas bacteria are not. Another form of pseudobacteria, 
mentioned by Cohn and Magnin, is the fibrine of the blood, which 
separates from that medium in the form of filamentous bacteria. 
This naturally reminds one of the explanation given by Mr. R. R. 
Greg, of the organisms found associated with diphtheria. He 
asserts that these are merely the different stages of the ordinary 
fibrillation of fibrine, viz. : micrococcus=granules of fibrine (first 
stage) ; rod-like bacteria=—fibrils of fibrine (second stage) ; spiral 
bacteria=spirals of fibrine (contractive stage). 
The characteristics that Prof. von Nageli relies upon for dis- 
tinguishing bacteria are,—“ spontaneous movement, multiplication, 
and equality of dimensions united with regularity of form.” The 
