198       Synthetical  Processes  in  Animal  Organism.  {AmAl>ru^889arm' 
Experiments  on  the  decomposition  products  of  proteids  have  in  no 
case  yielded  a  carbohydrate ;  and  not  only  that,  but  proteids  never 
yield  any  of  the  decomposition  products  of  carbohydrates  (lactic  acid, 
mucic  acid,  tartaric  acid,  etc.).  Still,  we  have  the  formation  of  gly- 
cogen taking  place  in  the  liver  when  no  food  but  albuminous  food  is 
taken. 
The  following  general  considerations  will,  however,  lead  to  a  better 
understanding  of  the  subject.  The  chemical  differences  between  ani- 
mal and  vegetable  cells  are  not  so  great  as  was  at  one  time  supposed. 
Their  chemical  composition,  so  far  as  it  is  known,  is  the  same ;  all  liv- 
ing cells  breathe  oxygen,  and  produce  carbonic  anhydride,  water  and 
amido-compounds.  If  the  synthetic  processes  are  more  highly  devel- 
oped in  chlorophyll-holding  plants,  that  does  not  mean  that  synthetic 
processes  are  absent  from  the  animal  cells.  As  instances  of  synthetic 
processes  in  animal  cells,  the  formation  of  hippuric  acid  from  glyco- 
cine  and  benzoic  acid,  or  of  ethereal  hydrogen  sulphates  from  phenol 
and  sulphuric  acid,  may  be  taken.  A  special  kind  of  synthesis  must, 
moreover,  occur  in  the  retrogressive  metamorphoses  of  proteids  which 
lead  to  the  formation  of  uric  acid  and  members  of  the  same  group. 
In  albumin  itself,  and  in  the  products  of  albumin  obtained  outside  the 
body,  the  number  of  carbon  atoms  is  much  greater  than  that  of  nitro- 
gen-atoms (indol,  leucine,  tyrosine,  etc.) ;  but  in  these  products  of 
metamorphoses  iu  the  body,  the  nitrogen  and  carbon  atoms  are  nearly 
equal  in  number,  or,  as  in  the  cases  of  urea  and  guanidine,  the  nitro- 
gen-atoms are  the  more  numerous.  The  importance  of  such  synthesis 
occurring  in  living  cells,  resulting  in  the  formation  of  cyanogen  con- 
taining molecules,  has  been  before  insisted  on  by  the  author. 
Researches  on  the  formation  of  fat  within  the  body  show  that  here 
again  there  are  undoubtedly  syntheses  occurring  as  the  result  of  the 
activity  of  liviug  cells ;  in  fact,  reactions  occur  which  cannot  be  re- 
peated in  the  laboratory  or  explained  by  any  known  chemical  laws ; 
they  are,  probably,  therefore,  the  result  of  a  breaking  down  of  mole- 
cules in  the  first  place,  and  the  living  cells  then  building  up  entirely 
new  materials  of  a  complicated  nature  from  the  simple  carbon  com- 
pounds so  liberated. 
The  carbohydrates,  for  example,  are  derivatives  of  the  hexatomic 
alcohol  C6H8(OH)6.  But  by  feeding  an  animal  on  starch,  the  fat  of 
the  body  is  increased,  and  substances  containing  chains  of  16  to  18 
atoms  of  carbon  linked  one  to  another  are  formed  ;  and  in  the  case  of 
