MORPHOLOGY AND PHYSIOLOGY OF BACTERIA. Ill 



called a capsule. The paired micrococci of pneumonia are 

 enclosed in such capsules. The capsule is more Ukely to be dem- 

 onstrated when the bacteria are obtained from the fluids 

 derived from an animal's body than when they have been 

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

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

 laginous 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 

 described 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 sarcinas from ^ 



micrococci depends upon fission in ® ® itr /i/ n r> 

 two or three planes. Repeated fissions " /»/ ml u 



of micrococci in one plane result in & Sj /^ 



the formation of streptococci. Micro- 



. ,1 , , ,, ,. . , , Fig. 43. — Bacteria WITH 



cocci that have recently divided are Capsules 



likely to be somewhat flattened on 



their opposing surfaces. Multiplication under favorable circum- 

 stances may take place at an exceedingly rapid rate. Bacilli 

 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)^*. 

 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 rapidly with the aniline dyes 





