SCOPE OF THE PROBLEM 



Lysozyme -f- stabilizer 



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Further incubation 



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Figure 3 A sketch visualizing the formation of spherical protoplasts 

 by lysozyme treatment of rod-shaped cells of Bacillus megaterium. 

 [From McQuillen, K. (1956), Symposium Soc. Gen. Microbiol., 6, 129 

 (1956); with permissio7i.~\ 



organisms do not show selective impermeability to small solute mole- 

 cules (cf. Roberts et al., 1957), but this view meets much opposed 

 evidence (cf. Mitchell and Moyle, 1956). 



Accepting then the presence at or near the cell surface of a 

 barrier that does not prevent the migration of water but which 

 minimizes sodium-ion penetration and at which the sodium ion 

 that does penetrate is extruded, we may test the proposition that it is 

 this same barrier that controls the entrance of other solutes or that 

 confines a phase into which solutes, in addition to potassium ion, 

 are concentrated. The principal difficulty is to prove that the accu- 

 mulated solute is really free and unmodified in the internal phase. 

 For this reason, the reality of active transport into the cell cannot 

 perhaps be placed on as firm a ground as can the concentrative na- 

 ture of secretion from one extracellular phase to another. Some of 

 the evidence on this question will be considered in Chapter 2. 



1 1 



