The categories that pathogenic organisms are placed. There are two general classifications with several subclasses for each: 1. plants: (a) bacteria (bacillus, coccus, spirillum), (b) rickettsia, (c) virus, (d) fungus (molds and yeasts); 2. Animals: (a) protozoa (amoeba, plasmodium), (b) spirochete, (c) metazoa (roundworm, tapeworm, trichinella), (d) schistosomes.