One of the amazing explorations in the field of microscopy is the actual circulation of the blood in the vessels of a living creature. When studying blood of animals, the microscope must be focused on a thin, transparent structure where blood vessels can be observed through the skin of the animal.

The tail is the most excellent point for microscope observation in the fish, while in the frog, its web of skin between the toes of the foot provides a window through which the microscopist can look into the complex network on the blood stream of the animal. The following microscopic technique applies to a fish, but it may also be adapted to a frog.

Obtain a 3×6 narrow piece of cardboard or thin wood. Cut out a round opening about one half inch across at one end of the board. A goldfish is a good example for microscopic observation because they are too small and are available anywhere. The following procedure while performing microscopic observation of the animals blood should be followed in order to keep the animal alive.

Moisten a piece of cloth or absorbent cotton in aquarium water. Wrap the fish loosely leaving its tail exposed. Position the fish on the prepared board with its rail set over the hole in the end. Spread its tail outwards and using a pin or thumbtacks, fasten it over the hole. Nail the moistened cloth or cotton to the board and place the board on the microscope stage exactly where the microscope glass slide is being set during observation.

Examine carefully and there will appear a network of blood vessels that flow through the tail of the fish. The transparent capillaries will now show the rush of blood. Using a high powered microscope, observe the specimen again, and focus carefully on the individual cells being swept along in the flow of the bloodstream. Observe that the tiny blood vessels are wide enough allowing its blood corpuscles to slip by.

During your microscopic observation, add a drop of aquarium water to the tail every few minutes to prevent the delicate tissues from drying out. Also, the cloth must be kept moist. If microscope study is limited only to a period of twenty minutes, the fish can still be returned to the aquarium unharmed.