BACTERIA. 157 



absorption is here in reality a digestive process, and results in the 

 in-taking of food. 



{d) Circulation. — Nothing to be noted. 



{e) Respiration. — The organs of respiration are on the whole 

 body surface. The lower we descend in our study of Biology the 

 more do we find every function performed indifferently by every 

 part. Nothing is specialised. The whole body breathes, repro- 

 duces. 



(/J Secretion. \ ^, . , . u . j- j 



/ N TIT o X There is nothing to be studied 



M Nervous System. /- , , i 



,j\ « « under these heads. 



{h) Sense-Organs. ^ 



(/) Motor Organs.— I would here warn the student against a 

 movement noticeable in these organisms that he will be apt to regard 

 as due to life. It is highly important not to confound the two 

 kinds of motion. That of dead matter is merely mechanical, not 

 vital, and resembles somewhat the swinging motion of a pendulum, 

 or that of " a floating buoy round its mooring." This movement 

 can be seen whenever any very small particles of matter, living or 

 dead, are suspended in a liquid. Very finely-divided charcoal, 

 camphor, cinnabar, or gamboge, if placed in water, will exhibit 

 similar movements. It is called the Brotvnian movement^ after 

 Brown, who thoroughly investigated it. It is simply a molecular 

 movement, due to mechanical, not to vital causes. Some of the 

 Bacteria only show this motion, and are then said to be in the 

 still stage. As in this condition they are usually surrounded by a 

 quantity of jelly-like material, this stage is known as the zoogl(ea 

 stage. Very often these organisms are in an actively mobile con- 

 dition, and undergo movements of translation from place to place. 

 The cause of these movements is in most cases not known. It is 

 possible they may result from the general contractility of the pro- 

 toplasm. But in Spirillum volutans, at each end a cilium or long, 

 fine, hair-like process has been seen, and by the movement of the 

 cilium that of the Spirillum as a whole is effected. Vibrio has a 

 wriggling motion, which is really due to its having a zigzag 

 arrangement of its joints, and also a rotation upon its own axis. 

 Bacillus is always free-swimming. 



