lO GENERAL MORPHOLOGY AND BIOLOGY 



with growth in particular surroundings. In some species the presence of 

 granules is an indication of lowered vitality. 



Whatever the compo'sition and relationships of the essential parts of the 

 bacterial protoplasm may be, there is, as has been said, reason for 

 believing that even in the lower forms reserve material exists. This 

 may consist of fat, glycogen, and other substances, amongst which may 

 be mentioned volutin, as described by A. Meyer, a substance probably of 

 proteid nature characterised by solubility in water, alkalies and acids, and 

 by insolubility in alcohol. 



In perfect healthy and young bacteria, appearances of granule 

 formation and of vacuolation maybe at tificially produced by physical 

 means from the occurrence 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 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 

 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 more readily observed in old or 

 otherwise enfeebled cultures. 



Biitschli, from a study of some large sulphur-containipg 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 bacillus, 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. The chemical 

 structure of bacterial protoplasm has been investigated both by 

 micro- and macro-chemical methods, the former being chiefly 

 applicable to the larger forms. With iodine, granules staining 

 brownish red or blue have been observed, and these are looked 

 on as composed of substances allied to glycogen and starch 

 respectively. Similarly, reactions with osmic acid, Scharlach and 

 similar dyes, have pointed to the presence of fats. While 

 macro-chemical investigation has not thrown much light on the 

 occurrence of carbohydrates, cellulose is said to be obtainable 

 from certain bacteria. Bodies giving the reactions of fats have 

 been isolated in bulk and have received much attention in the 

 case of the tubercle bacillus group, whose special staining char- 

 acteristics are probably due to bodies of this class. The 

 substances mentioned are to be looked upon as reserve material 

 or metabolic products in the life of the bacterial cell ; but 



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

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



