i 4 PRINCIPLES OF GENERAL PHYSIOLOGY 



out Investigations, especially by Hardy (1899, pp. 201-210) and by Alfred 

 Fischer (1899, pp. 1-72 and 202-336), have shown, on the contrary, that the 

 structures obtained in this way are produced by the reagents used, and that 

 quite different appearances are found in the same kind of cells according to 

 the fixing substance used. A few facts will suffice to demonstrate this fact. 



Flemming, in 1882 (pp. 50 and 51), noticed that the cell-sap of Spirogyra, which was a clear 

 liquid containing particles in Brownian movement during life, became a rigid network after 

 treatment with osmic acid (Fig. 12). 



Alfred Fischer (1899, p. 34) takes a clear solution of albumose and acts upon it with various 

 fixing reagents, obtaining various kinds of structures, as shown in Fig. 13. 



^Moreover, a homogeneous mixture of albumose and serum albumin, treated by Altmann s 

 osmic and bichromate mixture, gave a structure consisting of granules embedded in a 

 matrix of a fine reticular structure. These two structures could be stained in different 

 colours by the usual histological methods (Fischer, op. cit., p. 53, and Fig. 5 of the plate 



in his book). 



Again, if a mixture of different sizes of granules of the same substance, say albumose 

 precipitated bv platinum chloride, be stained with methyl green and fuchsin, the large granules 

 can be stained green, and the smaller ones red, or vice versa (Fig. 20 of Fischer's coloured 

 plate. Similar figures are reproduced in monochrome in our Fig. 14). 



Thus, after fixation, neither the form nor the staining properties give correct 



information as to the relationship of the con- 

 stituents of the original system. 



Hardy has shown (1899, pp. 163 and 184) 

 that when substances similar to protoplasm in 

 many of their properties, such as gelatine or 

 egg-white, are acted on by fixing reagents, a 

 separation of the solid from the liquid occurs, 

 so that the former is obtained as some kind of 

 a framework which holds the liquid portion (or 



- "phase") in its interstices. Now there are 

 FIG. 15. DIAGRAM TO ILLUS- ,. ' ... . , . , .. . 



TRATE RELATION OF PHASES IN two diflerent kinds of structures which it is 



COLLOIDAL SYSTEMS. of some importance to distinguish from one 



If the black be regarded as the solid phase, another. When a 13 per Cent. Solution of 



the white as the liquid phase, then A o-ploHnp is allowpd to " set, " bv roolino- there 

 represents an ordinary hydrosol, such as gelatine IS ailOWCC t oy C .lllg, Ul 



that of gold, in which the solid particles is a separation of the solid from the liquid 



are freelv movable. B represents a gel .v A L v. J 



of an alveolar or honeycomb structure, phase, but the latter cannot be squeezed out 



in which liquid drops are imprisoned by even by a pressure of twenty-six atmospheres, 

 more or less solid walls, such as a strong * ./ /. . uuj 



solution of gelatine when cooled. Whereas, if the jelly be fixed by tormaldehyde, 



the liquid can be pressed out by hand. The 



two kinds of structures are known as vesicular and sponge-like. The essential 

 difference is that in the former the liquid phase is in separate droplets each 

 surrounded by a continuous film of the solid phase; in the latter, the two phase* 

 are reversed in position : the solid phase is in the form of a network of threads, 

 while the liquid phase is continuous. A substance, therefore, which passes 

 through a membrane of the former structure has to penetrate through the 

 solid phase itself, while in the latter structure it can pass, although by a 

 tortuous route, from one side to the other by means of the liquid phase only. 

 In the language of colloid chemistry, one may also put it in this way : The 

 dispersed phase in the one is in the position of the continuous phase in the 

 other, and vice versa. The continuous phase is also called the external phase, 

 and the dispersed phase the internal one. The relationship between the two 

 forms of distribution may be made clearer by the diagram of Fig. 15, where 

 the black represents the one phase and the white part the other phase. If 

 black is solid and white is liquid, diagram B will represent the vesicular or 

 foam structure, and A the network or reticular structure in section. The 

 diagram A also represents an ordinary colloidal solution or an emulsion, if the 

 black areas are supposed to be solid or immiscible liquid respectively. 



Different fixing reagents produce, then, different kinds of structure in gelatine. 

 Alcohol or mercuric chloride gives a vesicular or foam structure and formaldehyde 

 an open network, as we have seen. 



