Am.  Jour.  Pkarm. 
April,  1889. 
Photography. 
199 
stearic  acid,  at  least,  we  have  a  number  (16)  which  is  not  a  multiple  of 
6.  By  this  synthesis,  too,  we  have  substances  which  possess  the  prop- 
erty of  circular  polarization  changed  into  those  which  are  optically  in- 
active. The  first  change  must,  however,  be  a  process  of  reduction; 
metabolic  changes  must  occur,  and  no  nutrient  material  stimulates 
metabolism  like  proteid ;  this  explains  why  feeding  on  starch  mixed 
with  a  small  amount  of  proteid  produces  fat,  and  without  it  will  not. 
The  proteid  mixture  is,  however,  so  small  that  it  alone  will  not  ex- 
plain the  great  increase  in  fat.  In  other  parts  of  the  animal  king- 
dom there  are  similar  occurrences  ;  for  instance,  the  formation  of  bees- 
wax from  honey.  Another  sample  of  the  same  kind  is  the  formation 
of  fat  from  proteid,  although  this  is  not  so  well  proved  as  the  forego- 
ing cases.  In  the  synthesis  of  fat  from  carbohydrate,  the  group 
Crl'OH  must  be  changed  into  CH2;  and  in  the  formation  of  carbo- 
hydrate (glycogen)  from  proteid,  the  group  CH2  must  be  changed  into 
CITOH  ;  in  both  cases,  numbers  of  these  groups  become  linked  to- 
gether. 
The  close  resemblance  between  animal  and  vegetable  cells  is  further 
shown  by  the  fact  that  many  lower  plants  (bacteria,  moulds,  etc.),  not 
only  flourish  in  solutions  of  albumin  and  sugar,  but  actually  shed  out 
ferments  to  convert  porteid  into  peptone,  and  starch  into  sugar,  and 
thus  aid  absorption.  They  breathe  oxygen,  produce  carbonic  anhy- 
dride, amido-derivatives,  and,  without  the  aid  of  sunlight,  fat,  carbo- 
hydrate and  proteid.  Nageli  (Sitzber.  Bair.  Akad.  Wissensch.,  1879) 
has,  however,  shown  that  these  fungi  will  assimilate  carbon  from  com- 
pounds in  which  it  is  combined  with  hydrogen  (amines,  etc.),  but  not 
from  those  where  it  is  combined  with  nitrogen  (cyanogen). 
PHOTOGRAPHY. 
BY   F.   V.  BtJTTERFIELD. 
(Concluded  from  page  158.) 
This  paper  would  be  still  incomplete  without  a  slight  reference  to  a  few 
of  the  many  useful  applications  to  which  photography  has  been  already  ap- 
plied. Besides  its  extended  use  in  portraiture,  it  has  rendered  invaluable 
service  in  astronomy,  and  paradoxical  as  it  may  seem,  nebulae,  etc.,  have 
been  photographed  whose  existence  was  utterly  unknown,  being  invisible 
through  the  most  powerful  telescopes,  until  still  larger  were  recentl}<  con- 
structed, when,  on  a  careful  examination  of  that  portion  of  the  heavens  in- 
dicated, the  evidence  of  the  sensitive  photographic  plate  was  fully  borne 
