IV] AND STRUCTURE OF THE CELL 303 



who sees threads where another sees channels is hkely to tell a 

 different story about neighbouring and associated things. 



It has also been suggested that the spindle is somehow due to a re-arrange- 

 ment of protein macromolecules or micelles ; that such changes of orientation 

 of large colloid particles may be a widespread phenomenon; and that coagu- 

 lation itself is but a polymerisation of larger and larger macromolecules*. 



But here we have touched the brink of a subject so important that we must 

 not pass it by without a word, and yet so contentious that we must not enter 

 into its details. The question involved is simply whether the great mass of 

 recorded observations and accepted beliefs with regard to the visible structure 

 of protoplasm and of the cell constitute a fair picture of the actual living cell, 

 or be based on appearances which are incident to death itself and to the 

 artificial treatment which the microscopist is accustomed to apply. The great 

 bulk of histological work is done by methods which involve the sudden killing 

 of the cell or organism by strong reagents, the assumption being that death 

 is so rapid that the visible phenomena exhibited during life are retained or 

 "fixed" in our preparations. 



Hermann Fol struck a warning note full sixty years ago: "II importe a 

 I'avenir de I'histologie de combattre la tendance a tirer des conclusions des 

 images obtenues par des moyens artificiels et a leur donner une valeur intrin- 

 seque, sans que ces images aient ete controlees sur le vivantf." Fol was 

 thinking especially of cell-membranes and the delimitation of cells; but still 

 more difficult and precarious is the interpretation of the minute internal net- 

 works, granules, etc., which represent the alleged structure of protoplasm. 

 A colloid body, or colloid solution, is ipso facto heterogeneous; it has after 

 some fashion a structure of its own. And this structure chemical action, 

 under the microscope, may demonstrate, or emphasise, or alter and disguise. 

 As Hardy put it, "It is notorious that the various fixing reagents are co- 

 agulants of organic colloids, and that the figure varies according to the reagent 

 used." 



A case in point is that of the vitreous humour, to which some histologists 

 have ascribed a fairly complex structure, seeing in it a framework of fibres 

 with the meshes filled with fluid. But it is really a true gel, without any 

 structure in the usual sense of the word. The "fibres" seen in ordinary 

 microscopic preparations are due to the coagulation of micellae by the fixative 

 employed. Under the ultra -microscope the vitreous is optically empty to 

 begin with; then innumerable minute fibrillae appear in the beam of light, 

 criss-crossing one another. Soon these break down into strings of beads, and 



* Cf. J. D. Bernal, on Molecular architecture of biological systems, Proc. Boy. 

 Inst., 1938; H. Staiidinger, Nature, Aug. I, 1939. 



t H. Fol, Becherches sur la fecondation et le commencement de VMnogenie chez 

 divers animaux, Geneve, 1879, pp. 241-242. Cf. A. Daleq, in Biol. Beviews, iii, 

 p. 24, 1928: "II serait desirable de nous debarrasser de I'idee que tout ce qu'il 

 y a d'important dans la cellule serait providentiellement colorable par I'hematoxy- 

 line, la safranine ou le violet de gentiane." 



