28 



MORPHOLOGY 



Fig. 11. — Electron Micrographs of Pneumococci (x 11,000). 

 A and B showing the capsule as a delicate light halo, and continuity of protoplasm 



in between the two cocci in A, and of cell wall in B. (Mudd et al., 1943a.) 

 C showing the capsule as a demarcated halo. {Mudd et al., 19436.) 

 (From micrographs kindly supplied by Dr. Stuart Mudd.) 



few years ago there was some doubt whether a definite external membrane limited 

 the ectoplasm (Legroux 1925, Legroux and Margrou 1920). The microdissection 

 of bacteria performed by Wamoscher (1930) suggested a definite elastic outer 

 layer, distinct from the inner material of the bacterium. 



Fischer (1894) studied the effect of hypertonic salt solutions on bacteria. The 

 cell contents were observed to shrink, leaving what appeared to be a rigid cell 

 wall of the same shape as the bacterial cell before treatment. These plasmolytic 

 experiments have since been repeated by many observers (see, for example, Knaysi 

 1930), but their significance as evidence for a definite limiting membrane in the 

 bacterial ectoplasm has been obscured by the possible artificial nature of the 

 structures produced. The differences of opinion (Legroux 1925, Legroux and 

 Margrou 1920) are to a large extent resolved by results of recent demonstrations, 

 by various independent techniques, of a definite cell wall. 



The changes in the cell wall during the division of bacilli have been studied 

 in detail by Knaysi (1941). Prior to the division of an elongated mother cell 

 into two daughter cells, he observed first a break in the cytoplasmic membrane, 

 and a centripetal movement of the cytoplasm. At the line of demarcation between 

 the cytoplasmic masses of the two daughter cells, a double intercellular plate 

 was deposited, which formed the two adjacent end walls of the completed daughter 

 cell. In a yeast, the deposition of the two walls preceded the cytoplasmic division. 



