SYMPOSIUM ON COLLOIDS 49 



Kite (3), in work marked by excellency and delicacy of tech- 

 nique, has done much toward answering this question. By 

 using an adaption of the Barber pipette as a dissecting knife he 

 has cut away various portions of a considerable number of dif- 

 ferent sorts of plant and animal cells, determining the con- 

 sistency, elasticity, and other physical characters of various 

 cell organs. His work shows that protoplasmic parts are much 

 more frequently gels than is generally supposed, and that the 

 same organs in cells of different organisms may have very dif- 

 ferent characters. The nucleus of Asterias egg is a free flow- 

 ing sol covered with a very tough consistent membrane and 

 bearing a nucleolus of rigid cohesive granular gel. The nucleus 

 of Spirogyra is a gel of rather slight viscosity bearing a net- 

 work of granules and strands of greater consistency. The 

 nucleus of epithelial cells of Necturus is a gel of greater viscos- 

 ity bearing areas of rigid granules, giving an appearance of 

 threads. Chloroplasts and many other organs show great 

 range of viscosity, varying from sols to consistent gels. Kite 

 finds that in general the animal cells are more viscous and con- 

 sistent than the corresponding organs of plant cells. 



There is no reason for believing that there is a transforma- 

 tion from gels to sols and vice versa, with a change of condi- 

 tions in protoplasm as in vitro. The conditions important in 

 producing such transformations are temperature changes, 

 changes in hydrogen, hydroxyl, and salts ion content. 



As to the second question — structure of gels — there are two 

 rather distinct pictures. One was developed by Biitschli and 

 confirmed and extended by Van Bemmelen (2, p. 10). They 

 consider gels to be solid colloids with solid dispersal medium 

 and fluid disperse phase. This is Butschli's well-known foam 

 structure. The frame work of the gel consists of the gel form- 

 ing materials with little water imbibed, surrounding numerous 

 spherical cavities filled with a water rich hydrosol of the gel 

 forming material. This foam structure can be seen with the 

 microscope in many hydrogels, especially after displacing the 

 water with alcohol or after slight drying. The mesh size of 

 the foam structure varies considerably with the sort of gel 

 studied and in some is apparently ultramicroscopical. The 

 people holding this view of gel structure extend it to hydrosols 

 as well, so even the more fluid portions of the protoplasm 

 are conceived as foam-like. 



This picture of hydrosols is very different from the more 

 strictly colloidal conception (1: pp. 312-316). According to 

 the latter view hydrosols consist of discrete particles of the 

 colloid dispersed in water. In the hydrophyllous group the 



