The  question  is  often  asked,  What  are  the  characters  of  the  true
cancer-uell  ?  or — Has  the  microscope  discovered  any  strnctnre  which


STRUCTURE  OF  CANCERS.  809

IS  decisive  of  cancer,  wherever  it  is  found  ?  The  answers  may  be— (1.)
Where  cells,  such  as  are  described  at  pp.  613  and  715,  are  fonnd  alone,
or  chiefly  composing  a  tumour,  we  may  be  certain  that  the  tumour  is  a
cancer:  we  may,  therefore,  regard  these  as  especially  cancer-cells.
(2.)  When  a  tumour  is  composed,  chiefly  or  alone,  of  corpuscles,  such
as  the  nuclei  described  at  p.  665,  or  any  others  which  we  can  trace
as  rudiments  or  degenerations  of  the  cancer-cells,  the  diagnosis  of  can-
cer  is  not  less  certain  :  structures  such  as  these  are  found  composing
none  but  cancerous  tumours.     But  if  the  question  be  changed  to— Are

there  any  cancers  which  are  not  formed  of  structures  such  as  these  ?

the  answer  must  be  afiirmative  :  for  there  are  rare  tumours  which  pre-
sent the  whole  clinical  history  of  cancers,  and  which  should  therefore
be  called  by  the  same  name,  though  they  have  not  these  peculiar  cancer-
structures,  or  have  them  in  very  subordinate  quantity.  I  do  not  refer
here  to  cancers  of  which  all  the  structures  are  imperfect,  or  degenerate,
or  diseased ;  but  to  such  as  the  fibrous  cancers  (p.  628),  the  osteoid
(p.  754),  and  certain  varieties  of  the  medullary  (pp.  666,  667).'
These  aU  deviate  from  the  assumed  specific  cancer-structures  ;  and  two
of  these,  the  fibrous  and  osteoid,  approximate  to  the  characters  of
natural  tissues.
