10 GENERAL MORPHOLOGY AND BIOLOGY 



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, in certain cases, of Polkorner may thus 

 be brought about. Plasmolysis in bacteria has been extensively 

 investigated, 1 and has been found to occur in some species more readily 

 than in others. Furthermore, it is often most readily observed in old or 

 otherwise enfeebled cultures. 



Biitschli, from a study of some large sulphur-containing forms, con- 

 cludes 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 Biitschli's preparations as due to plasmolysis. 



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_gramiles areTalso 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 production 

 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. Thus, for example, 

 if the b. pyocyaneus be exposed to the temperature of 42 C. 

 for a certain time, it loses its power of producing its bluish 

 pigment. Pigments formed by bacteria often diffuse out into, 

 and colour, the medium for a considerable distance around. 



Comparatively little is known of the nature of bacterial pigments. 

 Zopf, however, has found that many of them belong to a group of 

 colouring matters which occur widely in the vegetable and animal 

 kingdoms, namely, the lipochromes. These lipochromes, which get their 

 name from the colouring matter of animal fat, include the colouring 

 matter in the petals of Ranunculacese, the yellow pigments of serum and 

 of the yolks of eggs, and many bacterial pigments. The lipochromes are 

 characterised by their solubility in chlorolorm, alcohol, ether, and 



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

 " Ueber den Bau der Cyauophyceen mid Bakterieu," Jena, 1897. 



