Physiology: Effect of common drugs on Daphnia.

Daphnia is the common water flea. It is useful in this study of physiology because it reacts to the three common drugs we are investigating in this exercise. You will have to find the heart in your experimental subject. Adjust the condenser of your microscope to get the best contrast, then try to find the heart as shown in this photograph:

You will use three drugs in today's exercise. The drugs are labeled 1, 2, and 3, so you don't know which is which. This is typical of a double blind experiment in which neither the subject nor the experimenter know what to expect. The three drugs you will use are:

Ethyl alcohol (ethanol; grain alcohol) has a general depressive effect on nerve transmissions. Some nerve tissues are more sensitive than others. In general, ethyl alcohol has anaesthetic effects and slows heart rate.

Diphenhydramine is the major active ingredient in Benadryl. Usually, it's given to suppress secretion of mucus by the sinuses, or to suppress the itching and swelling associated with allergies. It can also be used to suppress motion sickness. It binds to histamine receptors on cell surfaces and blocks the action of histamine. It may cause some people to become sleepy, but ther people may become agitated or restless, and experience insomnia.

Caffeine is a common drug that stimulates the central nervous system, constricts the blood vessels, and stimulates the activity of the heart and lungs. Caffeine may affect the calcium ion balance in nerve cells, which could trigger transmission of nerve impulses.