8 BACTERIOLOGY FOR NURSES 



Mutations. Another and apparently inexplicable variation 

 sometimes appears which must be distinguished from the above. 

 Bacteria may lose or gain certain properties and the fact may be 

 explained by the minute divergence of successive generations. 

 Sudden changes or mutations occur, however, that cannot be thus 

 explained. 1 An instance is recorded in which daughter cells sud- 

 denly developed the power to ferment saccharose and raffinose. 

 During four years of successive transplanting the parent strain 

 did not acquire the property and the mutation strain did not 

 lose it. 



Structure of Bacterial Cell. The internal structure of bacteria 

 corresponds in simplicity to their external form. When examined 

 under the microscope in a living condition they appear as minute 

 colorless refractile bodies. In order to study their structure 

 advantage has been taken of their affinity for the various dyes 

 which are used to stain animal cells ; in this way several interest- 

 ing points have been determined. When stained the cell appears 

 finely granular or almost homogeneous. Many theories have 

 been advanced as to the nature of the cell substance or endoplasm. 

 The one most generally accepted is that the cell body consists 

 almost entirely of nuclear material with varying amounts of cyto- 

 plasm and that the nuclear material, instead of being gathered in a 

 compact mass or nucleus as in animal cells, is distributed through- 

 out the cell in a finely divided condition. 



Encircling the endoplasm is a covering of cytoplasm very simi- 

 lar in composition. The name ectoplasm is generally considered 

 more appropriate for this outer layer than cell membrane; it is 

 from this outer covering that the flagella or organs of locomotion 

 supposedly originate. 



In addition to the endoplasm and its covering of ectoplasm, many 

 bacteria, and perhaps all, are provided with a surrounding capsule 

 often of considerable thickness. Organisms in which it is specially 

 conspicuous present a more or less slimy appearance and appear 

 to be embedded in what seems to be a mass of jelly. Such a mass 

 is spoken of as a zooglcea mass; the individuals are known as 

 1 Jordan, Proc. Nat. Acad. of Science, 1915, 1, p. 160. 



