82 MORPHOLOGY AND CULTURE OF MICROORGANISMS 



at right angles with the long axis of the cell in the case of the bacilli 

 and spirilla, except in rare instances. In the case of micrococci, the 

 throwing of the cell wall across one diameter is 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 elon- 

 gate before division and micrococci divide before they elongate; 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 haK-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 woidd 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. 



Spore Formation. — A considerable number of bacteria form spores 

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

 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 ordiiiary 

 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 itseK with a spore 

 wall. At times the spore is smaller than the mother ceU 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 



