Such heterogeneous entities are evidently like mixed trash: such trash can�t be recycled. But by sorting�by putting cans in one pile, clear glass in another, plastic bottles in a third, and so on�recycling is made possible because each pile is then homogeneous or unmixed. Heterogeneous entities, identified by underlining, are discussed in the next five paragraphs.
The first substance found to cause cancer was coal dust. Both coal and oil are heterogeneous because each is composed of many different organic compounds�as are many things made from coal or oil, such as coal tar, which also causes cancer.
Other heterogeneous carcinogens include cigarette smoke (which contains over 4,000 different chemical substances) and smoke used as a food preservative. (The effect of heterogeneity isn�t limited to humans and explains why oil spills kill wildlife and smoking kills microorganisms in food.) Intestinal contents are extremely heterogeneous; that�s perhaps the basic cause of colon cancer. And a heat-treated sewage product, Milorganite, has been implicated in Lou Gehrig�s disease.
The stippled area at right contains a small quantity of silicone. [Sorry, we couldn�t actually replicate that attention-getting feature of our 1992 newsletter here on the Internet.] It�s a white, rubbery substance and seemingly uniform. But silicones are evidently heterogeneous on the molecular level: that may explain why silicone implants could cause immune problems. Another Si compound, the carcinogen asbestos, also seems heterogeneous to us because neither its chemical composition nor molecular structure is entirely constant or determinable. Breast-tissue lipids are heterogeneous; that might be a factor in breast cancer.
And cells can be heterogeneous. Mutated cells are an example: two cells on a person�s skin which have been mutated independently by ultraviolet light will have two different alterations of the normal skin cell DNA. Cells involved in reproduction�ova, sperm, and pollen�are also heterogeneous because of a cell division process, known as meiosis, which produces new gene combinations. If hay fever is incurable, the heterogeneity of pollen is probably the reason. And one might wonder if the meiotic heterogeneity of ova and sperm could be a factor in ovarian and prostate cancer respectively.
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