lO GENERAL MORPHOLOGY AND BIOLOGY. 



is placed in a solution containing 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 

 making a dried film for the microscopic examination of bacteria, the conditions 

 necessary for the occurrence of this process may be produced, and the appear- 

 ances of vacuolation and of Polkbrner may thus be brought about.- Plas- 

 molysis in bacteria has been extensively investigated,^ 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 very often either signs of degeneration, like the metachromatic granules, 

 or are artificially produced. They are most frequently observed in old or 

 otherwise enfeebled cultures. 



BUtschli, from a study of some large sulphur-containing forms, concludes 

 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 escapes notice, unless when, as in the bacilli, it can be made out at 

 the ends of the cells. Fischer, it may be said, looks on the appearances seen 

 in Butschli's preparations as due to plasmolysis. By special staining methods, 

 Nakanishi believes that he has been able to demonstrate, undoubtedly, nuclei 

 in a number of bacterial species. His work, however, has not yet been 

 confirmed. 



The Chemical Composition of Bacteria. — In the bodies of 

 bacteria many definite substances occur. Some bacteria have 

 been described as containing chlorophyll, but these are properly 

 to be classed with the schizophyceae. Sulphur is found in some 

 of the higher forms, and starch granules are also described as 

 occurring. Many species of bacteria, when growing in masses, 

 are brilliantly coloured, though few bacteria associated with the 

 production of disease give rise to pigments. In some of the 

 organisms classed as bacteria a pigment named bacterio-purpurin 

 has been observed in the protoplasm, and similar intracellular 

 pigments probably occur in some of the larger forms of the 

 lower bacteria and may occur in the smaller ; but it is usually 

 impossible to determine whether the pigment occurs inside or 

 outside the protoplasm. In many cases, for the free produc- 

 tion of pigment abundant oxygen supply is necessary ; but 

 sometimes, as in the case of spirillum rubrum, the pigment is 

 best formed in the absence of oxygen. Sometimes the faculty 

 of forming it may be lost by an organism for a time, if not 

 permanently, by the conditions of its growth being altered. 



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

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



