Informational film about organisms invading the blood. Shot of a cubicle bacillus multiplied 1000 times. Looks like a white blot. Narrator states several billions of organisms can overwhelm a body's defenses. The organisms looks like a tree branch. They are growing. CU of a cubicle bacillus that has grown. People are working with a substance on a glass slide in a laboratory. Person picks up an instrument in each hand, takes the substance and puts it in an incubator.