Studies on Capsule Formation: II. The Influence of Electrolytes on Capsule Formation by Klebsiella pneumoniae.

It was shown in a previous publication (Hoogerheide 1939) that Klebiella pneumonia (Friedla~nder's bacterium) is able to develop large capsules when allowed to grow in suitable media, and that, due to this abundant encapsulation, such cultures become very viscous. From a colloid-chemical point of view such an encapsulated culture may be considered as a suspension of small hydrophilic gel particles of polysaccharide nature, in a medium which itself is very poor in colloids. It seems, therefore, reasonable to assume that rules which have been found to be valid for hydrophilic sols and gels will be valid also, to a certain extent, for suspensions of encapsulated bacteria. In general, hydrophilic colloids maintain their stability due to the combined action of two factors: (a) the particles usually possess an electric charge (positive or negative), (b) the particles are more or less hydrated and surrounded by layers of water molecules which act as buffers in preventing union of two particles. Both factors not only determine the stability of such a hydrophilic colloid but also contribute to its viscosity. It is well known that the addition of small amounts of NaCl or other electrolytes to solutions of starch, agar-agar, casein or gelatin markedly decreases the viscosity of these hydrophilic colloids. Kruyt and co-workers (Kruyt-de Jong 1922, Bungen-