PLASMOLYSIS. 41 



size of the agglomerations being greater or smaller according to 

 the degree of development. 



In a few species of bacteria, colouring matter or ferric oxide is 

 stored in the mucinous envelope, further particulars of which will 

 be found in Chapter xxxiv. 



34. Plasmolysis. 



The difficulty of detecting the cell envelope of bacteria can be 

 removed by immersing the organisms in a solution of salt, which 

 exerts a hygroscopic action on the cell contents, in consequence 

 whereof they shrink and retreat from the cell wall, whereupon 

 the latter is readily recognisable, even in unstained preparations. 



This kind of influence, called Plasmolysis by H. de Yries, 

 was first observed in bacteria by De Bary, in connection with his 

 Bacillus megatherium. 



The experiment is simple in performance. An ordinary pre- 

 paration of the bacteria under examination is made, a few cotton 

 fibres being immersed to prevent the escape of the organisms. 

 The salt solution is then allowed to flow in at the edge of the 

 cover-glass, its transfusion being facilitated by absorbing the water 

 with blotting-paper held at the opposite side. Provided the 

 solution is not excessively concentrated, and that it contains no 

 toxic substance, the resulting plasmolysis in no wise destroys the 

 vitality of the cells. It can be made to disappear again by wash- 

 ing out the hygroscopic reagent. 



The concentration of the cell contents caused by plasmolysis, 

 which is also generally accompanied with an increased refractive 

 power, leads very often, as BUCHNER (I.) pointed out, to agglomera- 

 tions of material, which, unless more closely examined, might 

 illusively indicate the presence of endogenous spores. 



In such bacteria as are endowed with the power of locomotion, 

 the rate of movement is retarded by increased concentration of 

 the plasmolytic solution. WLADIMIROFF (I. and II.) entitled the 

 smallest percentage capable of arresting locomotion the critical 

 solution. The values of this for the various salts on any deter- 

 mined species of bacteria show an unmistakable regularity, the 

 chloride of any given metal (K, Na, &c.) having the weakest, 

 and the bromide and sulphate the strongest retarding effect, whilst 

 the nitrate occupies an intermediate position. As far as the bases 

 are concerned, potassium, sodium, and ammonium rank in the 

 order given. E. OVERTON (I.) has published several communica- 

 tions with regard to a number of substances which are unable to 

 effect plasmolysis owing to their passing through the plasma as 

 rapidly as water. 



The weakest solution of sodium chloride (NaCl) capable of 

 effecting plasmolysis is, according to A. FISCHER (I.), 0.5-0.75 

 per cent, for Cladothrix dichotoma, and for Crenothrix KuJiniana 



