CELL MEMBRANES 159 



sight of explanation on the grounds of the action of phosphoUpins 

 on surface tension. This is shghtly outside the confines of 

 microscopy, but it is very necessary to take as many facts into 

 consideration as possible. 



Cell Membranes. One of the problems which microscopists 

 have to face is connected with the nature of the cell and 

 nuclear walls. This question dates back to the discovery of 

 the cell in plants when the cellulose wall which w^e know now as a 

 secretion was regarded as the most important cellular structure. 

 Similar mistakes have occurred in animal cytology, especially in 

 connection with such specialised membranes as the vitelline 

 membrane of the egg. We are concerned now, however, with the 

 true protoplasmic wall. 



The advent of the technique of micro-dissection has been used, 

 chiefly by Chambers (21), to ascertain the nature of the restraining 

 cell wall. By means of the very delicate apparatus employed, it 

 is possible to touch delicately, puncture or tear the surface of 

 various cells contained in hanging drops. All the results point to 

 the fact that the cell wall is a definitely organised structure. This 

 is not to say, of course, that it is possible of isolation. As a matter 

 of fact, the reverse is the case. Its very organisation is dependent 

 not only upon the external medium, but upon the condition of the 

 protoplasm within. The chief proof of its organisation depends 

 upon the results of its destruction. If a mammalian (non- 

 nucleated) red blood corpuscle be punctured the haemoglobin 

 immediately begins to diffuse out over the whole surface of the 

 cell ; not merely at the point of puncture. The semi-permeability 

 of this membrane has been destroved all over by iniurv at one 

 point. Again, if the ciliated cells of the ovary of the sea-urchin 

 be punctured, disintegration of the cell wall takes place, com- 

 mencing at the break and rapidly spreads all over. The progress 

 of the degenerative process can be watched most successfully in 

 the ciliated region, as the cilia ceases to beat as soon as the wall 

 below has disintegrated. The time factor must not be neglected 

 as evidence. Portions of cells can be torn aw^ay from cells 

 (Amoeba, Lewis, vide 21) without permanent injury provided that 

 sufficient time is given for the surface film to organise itself. If, 



