88 MICROBES, FERMENTS, AND MOULDS. 
putrefaction. Those which are dead appear as small, 
rigid, and immovable rods. 
In observing the lively movements of these minute 
organisms, we might be tempted to regard them as 
animals. But we know that movement, taken by 
itself, is not peculiar to the animal kingdom. Setting 
aside the movement which can be provoked in the 
mimosa and in many higher plants, it is well to 
remember that many of the lower plants are capable 
of motion: this is the case with Diatomacee, in which 
the presence of chlorophyl incontestably proves their 
vegetable nature. The spores of plants of a much 
higher organization, such as ferns and mosses, have the 
power of swimming in the water, just as bacteria have: 
this has procured for them the name of Zoospores, 
although many of them contain chlorophyl. 
The movements of bacteria are, like those of zoo- 
spores, due to the presence of vibrating cilia, which 
are inserted at both extremities, or only at the hinder 
extremity of the microbe, and which form organs of 
propulsion analogous to the tails of tadpoles. These 
organs are very transparent: and are difficult to see in 
the living subject, even with the strongest magnifying 
power, on account of the rapidity of their movements, 
But their existence has been ascertained by the use of 
staining fluids, and above all by micro-photography. 
If, however, we analyze the mode of motion in 
Bacteriwm termo, and compare it with the movements 
of the ciliated or flagellated infusoria which may often 
