Diatoms and Diagnosis of Death by Drowning.

This thesis examines the diagnosis of death by drowning using the presence of diatoms in the organs of putative drowned subjects. A method of diatom extraction has been devised and evaluated which allows 100g samples of wet tissue to be treated. The organs are freeze-dried and then ashed at 550°C, and every effort has been made to reduce the risk of contamination by diatoms from reagents and glassware. Diatoms have been recovered from the organs of non-drowned subjects. These diatoms, which include Hantzschia amphioxys, Pinnularia borealis, Cyclotella comta and Melosira granulata, are commonly found on soil and other aeriel habitats, and can be swept into the air by air currents. The organs of non-drowned subjects also contained fragments of Coscinodiscus sp., which appeared to be of fossil origin. Many domestic products in normal use incorporate fossil diatomaceous earth containing fragments of Coscinodiscus sp. The ability of diatoms to enter the living mammalian body can be seen by examining the diatoms in the organs of seals. These animals are exposed constantly to diatoms in their environment, and consequently their organs normally contain many diatoms deriving from their marine environment. Diatoms also enter the organs during the drowning process, and it is imperative that the diatoms originating from the drowning medium toe differentiated from those which may have entered the body during life. Few diatoms were seen in the femoral bone marrow of drowned subjects, whereas diatoms from the drowning medium could often be found in the liver, brain and kidney. Many diatoms were usually found in the lung of drowned subjects. The presence of diatoms in the lung, and the presence of diatoms of the same species in other organs is an indication that drowning has occurred. If the "diatom method" is to be used, it is essential that contamination risks are kept to a minimum, that fossil and airborne diatom types are recognised and eliminated and that the diatoms are examined by an experienced diatomist. If these conditions are met, then the diagnosis of death by drowning using the presence of diatoms in the organs of putative drowned subjects is valid