Page:Once a Week Jul - Dec 1859.pdf/78

23, 1859.] a mouse — which Cardan  believed. Driven from the insect  world,  the  hypothesis  has  sought refuge in  the  world  of  animalcules  and  parasites; and there  the  hypothesis  is  not  so  easily  defeated. Who ever  turns  over  the  pages  of  old  Leeuwenhoek, the first  who  extensively  applied  himself  to  microscopic  observations,  will  see  that  the  Dutchman steadily set  his  face  against  Spontaneous  Generation, because  the  microscope  showed  him  that  many even of  these  minute  animals  had  their  eggs,  and were generated  like  the  larger  animals. Since that time thousands  of  observers  have  brought  their contributions to  the  general  stock,  and  each  extension of  our  knowledge  has  had  the  effect  of narrowing  the  ground  on  which  the  “spontaneous” hypothesis could  possibly  find  footing; the  modes of generation  of  plants  and  animals  are  becoming more and  more  clearly  traced; and  the  necessity in each  case  of  a parent-stock  is  becoming  more and more  absolute. It is  true  that  there  are organic beings  of  which,  as  yet,  we  can  only  say that there  is  the  strongest  presumption  against their being  exceptions  to  the  otherwise  universal rule of  generation. We do  not  know,  for example, how  the  Amoeba  arises; no  one  has ever seen  its  eggs; no  one  has  ever  seen  its  reproduction— and,  what  is  more,  it  is  perfectly  easy  to make  them  in  any  quantities. I have done  so repeatedly. Nevertheless, they  can  only  be  “made” under the  conditions  which  would  be  indispensable for their  birth  and  development  if  they  were  really generated from  eggs; and  that  they  are  so  generated is  a presumption  which  has  every  argument in  its  favour,  except  the  direct  evidence  of  the eggs themselves. The question  then  comes  to  this: Is it  more  probable  that  a law  of  generation  which is found  to  reach  over  the  whole  organic  world should have  an  exception,  or  that  our  researches have not  yet  been  able  to  detect  the  evidence which would  bring  this  seeming  exception  also under the  law? One after  the  other,  cases  which seemed exceptions  have  turned  out  to  be  none at all ; one  after  the  other,  the  various  obscurities have  been  cleared  away,  showing  one  law to be  general ; and  it  is  therefore  the  dictate  of philosophic  caution  which  suggests  that,  so  long as we  remain  in  positive  ignorance  of  the  actual process, we  must  assume  that  in  this  case  also  the general law  prevails.

Positive evidence  would  of  course  settle  the dispute ; but every  one  who  has  made  any  experiments, or  has  attentively  followed  the  experiments of others,  will  admit  that  it  is  excessively  difficult to devise  any  experiment  which  shall  be  conclusive. The facts  elicited  admit  of  such  different interpretations; the avenues  by  which  error  may enter are  so  numerous. I will not  narrate  here  the experiments of  Fray,  Gruithuisen,  Burdach,  Baer, and others,  since  they  cannot  withstand  serious discussion; nor -will  I adduce  my  own,  for  the same reason. But those  recently  made  by  M. Pouchet  have  a more  imposing  character,  and demand the  strictest  examination.

The reader  will  observe  that  the  cardinal  point in the  investigation  is  to  be  certain  that  no organic  germs  could  by  any  possibility  be  present in the  liquid  which  is  to  produce  the  animalcules. On the  hypothesis  that  the  animalcules,  like  other animals and  plants,  are  produced  from  germs,  or eggs,  these  germs  must  be  excessively  minute,  and easily overlooked. If they  exist,  it  is  in  the  water and the  air,  awaiting  the  proper  conditions  for their development. Supposing them  to  be  floating about in  the  air,  under  the  form  of  dust-like particles, they  would  fall  into,  or  enter,  any  vessel containing organic  matter  in  a state  of  decomposition, and  there  develope; as  the  deposited eggs  of  the  insect  developed  in  the  decaying  body of  the  dog. Now, inasmuch  as  the  presence  of atmospheric  air  is  one  of  the  indispensable  conditions of  vitality,  and  without  it  the  animalcules could  not  develope  and  live,  the  initial  difficulty is  how  to  secure  the  presence  of  this  air,  and  yet be sure  that  the  air  itself  does  not  bring  with  it the  germs  of  the  animalcules  which  we  find  in  the liquid. Schultze of  Berlin  devised  an  experiment which was  thought  to  have  finally  settled  this point, and  to  have  refuted  the  hypothesis  of  Spon- taneous Generation. An account  of  this  experi- ment, to be  found  in  the  “Edinburgh  New Philosophical Journal” for  October,  1837,  shows that an  infusion  of  organic  substances,  supplied with atmospheric  air,  but  not  with  an  air  containing living  germs,  was  suffered  to  remain  thus from the  end  of  May  till  the  beginning  of  August; but, during  the  whole  of  that  time,  no  plant  or animal  was  developed  in  the  infusion. The apparatus was  now  removed  from  the  flask, atmospheric air  was  allowed  to  enter  freely — without first  passing  through  the  acid  or  potass — and, in  three  days,  the  infusion  was  swarming with animalcules.

This really  looked  like  a conclusive  experiment. No sooner  were  measures  taken  which  would destroy the  germs,  supposed  to  be  suspended  in the  atmosphere,  than  the  infusion  was  kept  free from animalcules ; no  sooner  was  the  air  allowed to enter  the  flask  in  the  ordinary  manner,  than animalcules abounded. The proof  did  not,  however, seem  to  me  quite  rigorous. It was  by  no means  clear  that  the  air  in  its  passage  through sulphuric acid  would  not  suffer  some  alteration, perhaps electrical,  affecting  its  vital  properties; and this  doubt  seemed  confirmed  by  the  experiments of  M.  Morren,  communicated  to  the  French Academy, May  22,  1854; from  which  it  appeared that air  having  passed  through  sulphuric  acid  was incompetent to  sustain  life,  since  the  animalcules subject to  it  died  in  a few  days. But M.  Pouchet announces experiments  which,  if  correct,  not  only scatter this  doubt,  and  M.  Mori  on’s  confirmation, but point-blank  contradict  the  experiment  of Schultze. He declares  that  in  following  Schultze’s experiment in  every  particular,  and  also  in  repeating it  with  fresh  precautions,  he  can  constantly exhibit  animalcules  and  plants  developed  in  an infusion  in  which  every  organic  germ  has  been previously  destroyed,  and  to  which  the  air  has only  access  after  passing  through  concentrated sulphuric acid,  or  through  a labyrinth  of  porcelain fragments at  red-heat. Nay, M.  Pouchet  goes further. Feeling the  difficulty  of  satisfying  his opponents  that  the  atmospheric  air  really  contained no  germs,  he  determined  on  substituting artificial  air. This he  did  in  conjunction  with  a chemist,  M.  Hongeau. Artificial air,  as  the