Am.  Jour.  Pharm. 
Dec,  1891. 
Tuberculin. 
605 
other  hand,  a  50  per  cent,  solution  of  the  purified  tuberculin  in 
glycerin  appeared  to  be  very  stable.  From  a  consideration  of  its 
chemical  reactions,  and  the  results  of  three  elementary  analyses,  it 
would  appear  that  tuberculin  is  closely  allied  to  the  albumoses,  but 
differs  from  them,  and  especially  from  toxalbumen,  by  its  resistance 
to  high  temperatures  ;  it  also  differs  from  the  peptones  in  several 
respects,  especially  in  being  completely  precipitated  from  a  solution 
by  ferric  acetate.  From  the  results  of  a  number  of  physiological 
experiments,  made  first  upon  guinea  pigs  and  afterwards  on  human 
patients,  Dr.  Koch  has  arrived  at  the  conclusion  that  the  purified 
tuberculin  does  not  differ  markedly  in  the  nature  of  its  action 
from  the  crude  tuberculin,  but  that  the  former  has,  in  fact, 
diagnostically  and  therapeutically  the  same  effect  as  the  latter  when 
it  is  used  in  such  quantities  that  the  reaction  symptoms,  especially 
that  of  temperature,  attain  the  same  degree  of  intensity.  In  respect 
to  this  point,  it  has  been  found  that  whilst  the  action  of  purified 
tuberculin  upon  guinea  pigs  is  about  fifty  times  as  strong  as  that  of 
the  unpurified,  upon  human  patients  its  action  is  at  most  forty  times 
as  strong.  From  these  results,  therefore,  it  would  appear  that  Dr. 
Koch  and  his  coadjutors  have  not  been  so  successful  in  the  attempt 
to  purify  tuberculin  as  Dr.  William  Hunter,  wrho  claims  to  have 
succeeded  in  removing  from  it  the  constituents  giving  rise  to  fever 
and  inflammation,  leaving  a  product  which  in  the  hands  of  Dr. 
Watson  Cheyne  has  proved  capable  of  inducing  local  reaction,  fol- 
lowed by  healing  change  around  tuberculous  lesions,  unaccompanied 
by  any  constitutional  disturbance. 
In  an  appendix  to  this  communication,  Dr.  Koch  gives  some 
further  information  as  to  the  method  adopted  in  preparing  tuberculin. 
It  is  generally  understood  that  tuberculin  is  a  product  of  the  culti- 
vation of  tubercle  bacilli  obtained  in  the  form  of  a  glycerin  extract. 
As  may  be  supposed,  a  principal  difficulty  has  been  the  cultivation 
•of  the  bacilli  free  from  admixture  with  other  organisms.  Originally 
the  tubercle  bacilli  were  sown  upon  "  glycerinTpeptone-agar,"  and 
when  the  culture  had  attained  its  full  development  it  was  washed  off, 
collected  on  a  fine  wire  gauze,  extracted  with  a  4  per  cent,  glycerin 
solution,  the  solution  evaporated  to  one-tenth,  filtered,  and  the 
filtrate  used.  When  a  large  demand  arose  for  tuberculin,  the  agar 
cultivation  was  found  unsuitable,  as  it  gave  relatively  small  results. 
A  previously  abandoned  attempt  to  cultivate  the  bacilli  in  a  liquid 
