Essay --

The cations (Na+, K+ and Mg++) were estimated in the gut contents, fresh tissue of midgut epithelia and heamolymph of uninfected and Bacillus inoculated silkworm. The sodium level was declined from gut contents to heamolymph. The level of sodium content further showed a gradual decrease from the midgut tissue to the heamolymph in the infected silkworm as compared to the uninfected silkworm. The potassium content initially decreased from the gut contents to the midgut tissues in both the uninfected and infected silkworm (Table-1, Fig. 2). Later on, a slow gradient in the potassium content was observed from the midgut tissue towards the heamolymph in the infected larvae. But incase of the uninfected larvae the potassium content gradually declined from the midgut tissue to the heamolymph. In the present study the levels in sodium content was high and potassium concentration was low in tissue than reported earlier. The adult larvae of silkworm, showed a steep gradient for magnesium betwe en lumen and heamolymph, with higher concentration in the heamolymph (Table-1, Fig. 3). Table - 1. Ionic concentration in lumen content, fresh tissue and heamolymph of silkworm Bombyx mori V instar (meq/L). The ionic concentrations were changed in the Bacillus infected larvae. Flacherie resulted in the non-significant decrease of intracellular sodium in midgut cells. Potassium being the major cation in the silkworm diet showed a significant decrease in midgut cells in diseased larvae (p ...f silkworm Bombyx mori Electron micrographs illustrate the midgut of silkworm B. mori. The globlet cell (Plate - 1) wherein the multiplication of pathogen occurs and these cells are slightly elongated with a centrally located cavity. Their ill defined microvillae project into this cavity and these cells are placed in between columnar cells. Dominant cell in midgut epithelium is the columnar cell. The apical surface of the columnar cell is thrown into numerous folds and often appears as finger like projections (microvillae). A cross section of the microvillae, are presented (Plate - 2). The microvillae are located with mitochondria (Plate - 3), vacuoles at the base of microvillae are prominent. Excess of plasma membrane folds at the tip of the microvillae were observed in all the sections scanned. The midgut epithelium is richly supplied with trachea (Plate - 4).