122 MANUAL OF BACTERIOLOGY. 



grown artificially in culture-media. A zooglcea is a large mass 

 of bacteria in a resting condition held together by a mucilagi- 

 nous substance. The composition of bacteria varies con- 

 siderably with different species. The basis appears to be 

 proteid substance. 



Vegetative Cells. All the forms enumerated above are 

 called vegetative cells in contradistinction to spores to be de- 

 scribed later, and multiplication takes place by the direct 

 division or fission of these cells. In the rod-shaped bacteria 

 the fission is transverse. The formation of tetrads or sarcime 

 from micrococci depends upon fission in two or three planes. 

 Repeated fissions of microccocci in one plane result in the for- 

 mation of streptococci. Micrococci 

 that have recently divided are likely to 

 I n ^ e somewnat flattened on their op- 

 posing surfaces. Multiplication under 

 C """ ) favorable circumstances may take place 

 at an exceedingly rapid rate. Bacilli 



FIG. 45. Bacteria with , , , , ,. . , 



capsules. have been observed to divide in twenty 



minutes. If division takes place once in 



an hour, the progeny of one organism at the end of twenty-four 

 hours will be 16,777,216, i. e., (2 X i ) 24 . The ordinary form 

 of reproduction by fission is called vegetative, and bacteria that 

 are multiplying in this manner are often spoken of as being in 

 the vegetative condition. 



Spores. Under certain circumstances the reproduction of 

 bacteria takes place by means of the germination of bodies 

 called spores. These appear in a typical form in the large 

 bacilli, where, near the centers of the bacilli, highly refracting, 

 shining spots may be seen which are found to stain less readily 

 with the aniline dyes than the rest of the bacilli. They are not 

 to be confused with the unstained spots described as vacuoles. 

 On account of their being formed from a part of the interior 

 of the bacterium, such spores are called endogenous. These 



