I02 



MORPHOLOGY AND CULTURE OF MICROORGANISMS 



areas surrounding the bacteria. If, due to shrinkage of the bacteria, 

 dr other material on the preparation, clear spaces are formed, it is 

 readily seen that these might be confused with the real capsule. It is 

 possible to stain the capsules by special methods; these must be used in 

 order to determine positively the existence of the capsules. The 

 bacteria which grow in the bodies of animals frequently contain these 

 capsules but fail to show them when grown upon artificial culture media. 

 It is difficult, therefore, to determine whether or not an organism has a 

 capsule by mere examination of cultures. Some culture media, how- 





^;:;'- . 



Fig. 78. — Capsules. Bact. pneumonia (Friedlander). (After Weichselbaum from 

 Frost and McCamphell.) 



ever, do cause a formation of capsules in the case of capsulated bacteria. 

 These are blood serum, sometimes, and milk, usually. Beautiful cap- 

 sules can be obtained by growing such bacteria as the Bact. pneumonice, 

 BacL' capstdatum, and Bact. welchii in milk cultures. Strept. mesen- 

 teroides is a bacterium which grows in the syrup of the sugar refineries 

 and forms abundant capsules. This organism changes the char- 

 acter of the syrup, and its entrance and growth is frequently the cause 

 of serious loss. 



Flagella. — General Consideration of Flagella.* — The flagella are 

 very narrow thread-like structures. It is not known how narrow since 



♦ Prepared by W. D. Frost, 



