MINUTE STRUCTURE OF THE BACTERIAL CELL 57 



absorption of water, and if kept under such conditions for 

 any length of time the cell wall will rupture (rhexis) and the 

 protoplasmic and other contents escape into the surrounding 

 liquid (plasmoptysis). A six per cent solution of cane sugar 

 exerts a pressure of 3075 mm. of mercury at 14 degrees C. 

 (sixty pounds to the square inch). Just so, under natural con- 

 ditions, the form and structure of a bacterial cell may be al- 

 tered according to the character of the food and the density of 

 the surrounding medium. The phenomena of plasmolysis 

 and plasmoptysis doubtless account for the involution forms 

 among certain species and the so-called pleomorphism of 

 some cells. It may be said in this connection that it is im- 

 possible to subject all species of bacteria to the phenomenon 

 of plasmoptysis, due to the fact that their cell wall and 

 ectoplasm are so constituted that salts may diffuse out more 

 readily than in others. 



Metachromatic and Polar Granules. Under certain con- 

 ditions in some species of bacteria the cells show a peculiar 

 granular appearance when stained with the ordinary anilin 

 dyes. The granules are irregular in size, do not occur in any 

 definite arrangement, and stain darker than or at variance 

 with the surrounding protoplasm (Loeffler's methylene blue 

 stain on Bact. diphtherias) . These granules are known as 

 metachromatic granules. The protoplasm in these cases seems 

 to have a beaded appearance. There have been various 

 staining methods devised to demonstrate these granules. In 

 other species of bacteria there is a concentration of the pro- 



