BACTERIA. 43 



quite as economical as any other and may therefore proceed in any 

 direction. Migula makes a considerable point of the fact that bacilli 

 and spirilla elongate before division and micrococci divide before they 

 elongate, and this would be the criterion which he would use to separate 

 these two-form types. A generation among the bacteria is from one 

 division of the cell to another. This is sometimes very short, in fact, 

 only twenty to thirty minutes. Many of the bacteria after half-an- 

 hour's time have grown from newly formed cells to maturity and are 

 ready to divide again. This makes it possible for bacteria to multiply 

 with very great rapidity, and if we know the length of the generation in 

 a particular bacterium it would be easy enough to estimate the rate of 

 multiplication, at least theoretically. It would be only a matter of geo- 

 metrical progression. It is of course quite impossible for the bacteria 

 to maintain their theoretical rate of growth for any length of time, but, 

 practically, they grow with enormous rapidity, as is shown in cultures 

 and the changes which they bring about in nature, such as the produc- 

 tion of fermentation and the generation of toxin. 



SPORE FORMATION. A considerable number of bacteria form spores 

 within the cell. Because they are formed within the cell they are 

 spoken of as endospores. Endospores are formed by the bacilli and the 

 spirilla, but not by the micrococci. Their chief value to the cell is their 

 ability to resist unusual conditions, and to enable the individuals of a 

 species to pass through unfavorable conditions which to the ordinary 

 vegetative form of the cell would prove disastrous. At the maturity 

 of the cell, spore formation may begin. It is an open question whether 

 spore formation occurs as a regular stage in the life history of an organism, 

 or is produced only under the stimulus of unfavorable environmental con- 

 ditions. Both theories have their advocates. The first evidence of 

 spore formation in the cell is a granulation of the protoplasm of the cell. 

 As spore formation proceeds the granules become larger and collect at 

 one portion of the cell. These granules then fuse to form the spore, 

 which soon surrounds itself with a spore wall. At times the spore is 

 smaller than the mother cell and is formed without changing the shape 

 of the cell. At other times it is larger than the mother cell and causes a 

 bulging of the latter. The position of the spore in the cell varies (Fig. 24). 

 In some species it is equatorial, in others it is polar, and in still others it has 

 an intermediate position between the equatorial and polar. When the spore 

 is larger than the mother cell and is situated equatorially it causes the cell 



