S U R h A C i: S T 1< U C T U R li S 33 



By comparison of electron nncrographs of crushed or sectioned bacteria of 

 septate and non-septate morphology an independent verification of these 

 observations, made upon stained material, by classical microscopy, has now 

 been estabHshcd. 



B: THE CELL MEMBRANE 



(2, 3, 4, 8, 9, II, 15, 17, iS, 20, 21, 22, 26, 27, 31, 39, 41, 42, 43, 46, 57, sS, 65, 

 66, 67, 71, 72, 77, 81, X3, 86, 87, 88, 91, 98, 102, 103, 104) 



Little is known of the structure of the cell membrane. Extensive studies 

 have been made upon its physico-chemical behaviour, but diese are beyond 

 the scope ot the present work. A few observations have been made upon 

 its chemical constitution, but fewer than in the case of the cell wall. It appears 

 to be a semi-permeable membrane about lOO Angstrom units in thickness. 



Unlike the cell wall, the underlying cytoplasmic membrane, which 

 constitutes the osmotic barrier of the cell, is embarrassingly easily stained by 

 almost any method. This applies especially to the cytoplasmic septa and the 

 growing points, which are associated with the membrane. These structures 

 are highly basophilic, so much so that they will stain well with many dyes 

 supposedly specific for chromatin, mitochondria, reticulocytes, etc. The entire 

 cell membrane has a high content o( nucleoproteins, but these are especially 

 concentrated in the growing points, and it is interesting to consider the 

 observation of Pijper (1938) that somatic agglutination occurs by the adherence 

 of the bacteria at the tips of the cells. Not only is the cell wall very thin at 

 this point, being in the process of formation, but one of the main aggregations 

 of nucleoproteins in the cell membrane occurs immediately underneath, so 

 that it would appear that the growing points, and presumably also the almost 

 identical cytoplasmic septa, may be a major somatic antigen. 



The nucleic acids in the cell membrane are almost unquestionably res- 

 ponsible for the ease with which the entire bacteria can be stained, and when 

 tliis stainable cortex is viewed through the tips of the cell, the well-known 

 optical illusion of " bipolar staining " is observable, sometimes reinforced by 

 the appearance of the basophilic growing points. The nucleic acids are also 

 claimed to cause the phenomenon of Gram-positivity, where it occurs (Henry 



