84 MORPHOLOGY AND CULTURE OF MICROORGANISMS 



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 multiplica- 

 tion, at least theoretically. It would be only a matter of geometrical 

 progression. It is of course quite impossible for the bacteria to main- 

 tain their theoretical rate of growth for any length of time, but, prac- 

 tically, they grow with enormous rapidity, as is shown in cultures and 

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

 tion of fermentation and the generation of toxin. Four periods in the 

 life history have been described. A latent or lag period, which is the 

 time elapsing between the seeding and the time at which the maximum 

 rate of growth begins; the logarithmic period or the time when the rate 

 of growth is at its maximum; a stationary period when the increase 

 becomes less and less and finally ceases; and the period of decline when 

 the organisms begin to die. 



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 en- 

 vironmental conditions. 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 



