754  Chemical  Elements  of  Living  Matter.  |  AmNo°v!'i92iarm' 
ELEMENTS  OCCURING  RARELY  IN  LIVING  ORGANISMS. 
ip.  Lithium  occurs,  in  traces,  apparently  in  all  animals  and 
plants  and  seems  to  be  a  constant  constituent  resembling  the  other 
alkali  metals  in  its  function.  The  lungs  of  mammals  contain  lithium 
salts.  Lithium  compounds  are  rapidly  absorbed  and  eliminated  by 
the  kidneys — no  case  of  poisoning  has  so  far  been  recorded. 
20.  Rubidium  is  found  in  various  animals  and  plants. 
21.  Ccesium  occurs  in  traces  in  some  animal  organs  and  in  many 
plants  (timothy,  raspberry,  beets,  etc.). 
22.  Strontium  is  present  in  animals  and  plants  in  variable 
amounts  and  seems  to  be  of  accidental  occurrence. 
23.  Barium  is  found  in  some  plants  grown  on  soil  containing 
barytes. 
24.  Radium  occurs  in  minute  traces  in  animals  and  plants. 
25.  Boron  is  sometimes  found  in  the  ashes  of  plants,  especially 
if  grown  on  soil  rich  in  tourmalin  and  its  decomposton  products 
(Belgium,  So..  California). 
26.  Zinc  has  been  reported  in  the  human  liver  (10-76  mg.  per 
kg.)  ;  traces  are  also  found  in  corals  and  some  plants. 
27.  Copper,  while  not  essential  for  vertebrates,  occurs  in  the 
human  body;  especially  in  the  blood,  brain,  kidney  (1.2-2  mg.  per 
kg.),  spleen  (3.2-5.6  mg.  per  kg.),  liver  (1.5-15  mg.  per  kg.).  It  is 
essential  for  invertebrates  where  it  plays  the  same  role  which  iron 
does  in  vertebrates,  namely  as  respiratory  metal  and  oxygen  carrier 
in  the  form  of  hsemocyanin.  The.  bluish  blood  of  molluscs  (Cepha- 
lopoda and  Gastropoda)  contain  large  amounts  of  copper  (e.  g., 
oysters,  octopus,  lobsters,  helix  pomatia,  Limulus  cycleps  and  Sabella 
species).  It  has  also  been  found  in  the  plumage  of  a  bird,  the 
turaco  or  Cape  Lory,  whose  red  feathers  contain  turaein  (7%  Co.). 
28.  Nickel  and  29.  Cobalt  occur  in  traces  in  some  plants. 
30.  Chromium  is  occasionally  found  in  small  amounts  in  some 
plants. 
31.  Vanadium  is  exceedingly  rare,  found  only  in  few  cases. 
32.  Titanium  is  found  in  slight  traces  in  nearly  all  plants  and 
appears  to  be  a  constant  constituent  like  silicon. 
