Understanding Heat and Temperature

Our sense of touch tells us quite definitely that one body is hot and another cold. But this is a purely quali- tative criterion, not sufficient for a quantitative descrip- tion and sometimes even ambiguous. This is shown by a well-known experiment: we have three vessels con- taining, respectively, cold, warm and hot water. If we dip one hand into the cold water and the other into the hot, we receive a message from the first that it is cold and from the second that it is hot. If we th...

 The Immune System VS Viruses

The immune system consists of white blood cells that come in about 10 million different types. Each type has a protein lock on it called an "antibody," which corresponds to a key carried by a bacterium called an "antigen." If a key enters that lock, the white cell starts multiplying ferociously in order to produce an army of white cells to gobble up the key-carrying invader, be it a flu virus, a tuberculosis bacterium, or even the cells of a transplanted heart. But the body has a problem. It ...