[Illustration: FIG. 26.--Spores showing polar germination. The lighter part of the two organisms just below A and B is the developing bacterium. In the original slide the spore was stained red and the developing bacterium a faint blue.] [Illustration: FIG. 27.--A spore showing equatorial germination. The spore in the center of the field shows a rod growing out of it laterally. In the original slide the spore was stained red and the developing bacterium blue.] [Illustration: FIG. 28.--Spores in the middle of the rod without enlargement of the rod. The lighter areas in the rods are spores.] [Illustration: FIG. 29.--Spores in the middle of the rod with enlargement of the rod around them. The lighter areas in the rods are spores.] Spores are most commonly oval or elliptical in shape, though sometimes spherical. A spore may be formed in the middle of the organism without (Fig. 28) or with (Fig. 29) a change in size of the cell around it. If the diameter through the cell is increased, then the cell with the contained spore becomes spindle-shaped. Such a cell is termed a “_clostridium_.” Sometimes the spore develops in the end of the cell either without (Fig. 30) or with enlarging it (Fig. 31). In a few forms the spore is placed at the end of the rod and shows a marked enlargement. This is spoken of as the “_plectridium_” or more commonly the “drumstick spore” (Fig. 32). The position and shape of the spore are constant for each kind of bacteria. In one or two instances only, two spores have been observed in a single organism. [Illustration: FIG. 30.--Spores in the end of the rod with no enlargement of the rod around them. The lighter areas in the rods are spores.] [Illustration: FIG. 31.--Spores in the end of the rod with enlargement of the rod, _A_, _A_, _A_, _A_.] [Illustration: FIG. 32.--Drumstick spores at the end of the rod.] The fact that the protoplasm is denser and the spore capsule thicker (the percentage of water in each is decidedly less than in the growing cell) gives the spore the property of much greater resistance to all destructive agencies than the active bacterium has. For example, all actively growing cells are destroyed by boiling in a very few minutes, while some spores require several hours’ boiling. The same relation holds with regard to drying, the action of chemicals, light, etc. That the coagulation temperature of a protein varies inversely with the amount of water, it contains, is shown by the following table from Frost and McCampbell, “General Bacteriology”: Egg albumin plus 50 per cent. water coagulates at 56° „ „ „ 25 per cent. „ „ „ 74-80° „ „ „ 18 per cent. „ „ „ 88-90° „ „ „ 6 per cent. „ „ „ 145° „ „ dry „ „ „ 160-170°