50 ILLINOIS ACADEMY OF SCIENCE 



particles are more or less swollen by the absorption of water. 

 The advocates of this view extend this conception of hydrosols 

 to hydrogels. In the gel the imbibed or hydrated particles crowd 

 upon each other, giving high viscosity. 



It is estimated that in a 6 per cent casein solution the swol- 

 len submicrons or amicrons occupy about 60 per cent and in a 

 9.4 per cent solution about 80 per cent of the space of the total 

 solution. There are several reasons offered for postulating 

 this structure. Both a gelatin solution too dilute to gel and 

 one sufficiently concentrated to gel show numerous submicrons 

 as they cool, but no difference between the two can be detected 

 by the ultramicroscope. Each can be flocculated by salt addi- 

 tions with the same relative effectiveness of the ions. There 

 are points of similarity between the phenomena resulting from 

 mixing with water certain hydrating crystalloids like sulfuric 

 acid and glycerin and those of swelling gels. High dispersion 

 of these gels along with their hydration gives them many of the 

 characters of true solutions. The degree of dispersion of 

 gelatin is not known, but it is certain that haemoglobin forms 

 a molecular solution. 



It is not believed that the foam structure of Biitschli 

 and VanBemmelen is an ever present structure of gels. 

 It is considered that the foam structure is one of several de- 

 formations produced in gels by a variety of reagents or by 

 pressure and temperature changes. A number of work- 

 ers have studied separations of this type produced in gels 

 and sols. We may draw a good illustration from Hardy's 

 work (4). He found that when gelatin was treated with con- 

 centrated sublimate or other killing or fixing agents a variety 

 of structures appeared depending upon the concentration of 

 gelatin and the reagent used. From dilute solutions treated with 

 sublimate the gelatin falls out as individual granules, from 

 medium concentrations as a network of granules and in con- 

 centrations of 5-7 per cent or above a foam structure appears. 

 The more concentrated the gel the thicker the walls of the 

 foam and the smaller the enclosed cavities. In 10 per cent 

 gelatin the cavities were 7/x in diameter and in 50 per 

 cent gelatin 2.5 /* in diameter. These reactions were reversible 

 or irreversible, depending on the reagent used. Protoplasm 

 shows very similar behavior in all respects with perhaps a great- 

 er sensitive to reagents, both as to deformation and irreversi- 

 bility, and these reactions may in large part explain the vari- 

 ous theories of protoplasmic structures. It seems established 

 now that these reversible flocculations occur in normal living 

 protoplasm. The irreversible ones, if extensive, lead to death. 



