BACTERIA. 155 



find it best to infuse hay in warm water for thirty minutes ; filter, 

 and keep the filtrate in a warm place. Note the changes which go 

 on in it. At first clear ; in 24-36 hours it becomes turbid ; later 

 on, a scum forms [on the surface, and the infusion acquires a 

 putrcfiictive odour. One very common bacterium may be easily 

 procured — Bacterium teiuio, Dujardin ("Zoophyt," p. 212) ; (syno- 

 nyms, Monas ten/io, Miiller ; ? Palmelia Itifusiomim^ Ehrenberg ; 

 Zoog/cea fenno^ by Cohn) — by taking half-a-glass of ordinary 

 water from a spring or river, and leave it for some days on a table 

 or chimney-piece, the vessel being uncovered to allow free access 

 of air. The water from the top of a small aquarium will also 

 show them, or a small piece of meat kept in water at a moderate 

 temperature. 



2. — Size. They are very minute. Hence arises a great 

 danger of the confusion of other bodies with these on the part of 

 the student. The cells are shortly cylindrical, oblong, about 

 1 '5 — 2 /i long, with a flagellum at each end. 



3. — General Structure. They are masses of protoplasm of 

 various shapes, that are in many cases not surrounded by a dis- 

 tinct wall. Protoplasm is derived from Trpwrog — first, TrXaa/ia — 

 formative matter; i.e., matter that can be shaped into other 

 substances, such as the tissues of a plant or of an animal body. 

 It is semi-fluid, granular in appearance, and consists of four 

 elements— carbon,^hydrogen, oxygen, and nitrogen. It has the 

 power of contractility. The protoplasm adheres to iodine, and it 

 becomes brown. If the piece of protoplasm is without an 

 enveloping wall, as in many Bacteria, and consists of protoplasm, 

 and protoplasm only, we have a plasiid. If the protoplasm is 

 invested with a distinct wall — that is, wholly distinct of structure — 

 the being is a cytode ; for a cytode is a free mass of protoplasm 

 enveloped by a distinct wall. This wall is more transparent than 

 the contents. In the compound form it is only to be seen just 

 where the joints making up the compound form come in contact 

 one w^ith the other. In the still condition of these organisms the 

 wall is exceedingly gelatinous. This still stage, with its thick 

 envelope of jelly-like material, is known as the zoogloea stage 

 (Zwoj/ — life ; -{KoioQ — viscid). 



