12 GENERAL MORPHOLOGY AND BIOLOGY. 



rence of what is known as plasmolysis. To speak generally, 

 when a mass of protoplasm surrounded by a fairly firm 

 envelope of a colloidal nature is placed in a solution con- 

 taining salts in greater concentration than that in which it 

 has previously been living, then by a process of osmosis 

 the water held in the protoplasm passes out through the 

 membrane, and, the protoplasm retracting from the latter, 

 the appearance of vacuolation is presented. Now in mak- 

 ing a dried film for the microscopic examination of bacteria 

 the conditions necessary for the occurrence of this process 

 may be produced, and the appearances of vacuolation and 

 of polkorner may thus be brought about. Plasmolysis in 

 bacteria has recently been extensively investigated, 1 and 

 has been found to occur in some species more readily than 

 in others. We may conclude that such appearances as 

 vacuolation of the bacterial protoplasm and polkorner are 

 either signs of degeneration, like the metachromatic 

 granules, or are artificially produced. All of them are 

 most frequently observed in old or otherwise enfeebled 

 cultures. 



Biitschli has published interesting observations on the minute struc- 

 ture of some large sulphur-containing bacteria. These were found to 

 consist of an outer membrane enclosing the protoplasm, which was 

 divided into two parts an outer protoplasmic network containing bac- 

 terio-purpurin, and an inner part, the greater portion of the latter being 

 stained blue with hsematoxylin more deeply than the outer, in specimens 

 out of which the bacterio-purpurin had been dissolved. In this central 

 part thus stained there were red granules, which Biitschli regards as 

 the metachromatic granules of Ernst. The bacilli in the specimens he 

 examined seem, however, to have been healthy. Biitschli looks upon 

 the outer part of the central body as corresponding to the protoplasm 

 of an ordinary cell, the inner part as corresponding to the nucleus. 

 In one smaller bacterium he found evidence of the former only at the 

 end of the cell. He therefore thinks that the greater part of the 

 bacterial cell may correspond to a nucleus, and that this is surrounded 

 by a thin layer of protoplasm, which in the smaller bacteria probably 

 escapes notice, unless when it is specially abundant at the ends. This 

 terminal plasma has also been found by Wager in another bacterium. 



1 Consult Fischer, ' ' Untersuchungen iiber Bakterien," Berlin, 1894; 

 " Ueber den Bau der Cyanophyceen und Bakterien," Jena, 1897. 



