Ever since Leeuwenhoek first revealed the world of "little animals" or protozoa, man has been interested in these one-celled creatures who amazingly perform all the biological functions of birds, insects and even whales. It was the variety, the forms, and the movements of the protozoa that at first intrigued microscopists. As researchers became better acquainted with them, however , it was discovered that the growth, health, sickness and death of protozoa and man are closely interconnected.