300 THE BEGINNINGS OF LIFE. 



existence in that solution of certain crystalline germs; 

 and similarly that living things can arise in no solution 

 whatsoever without the pre-existence in such solution 

 of living germs? The very mention of this question 

 in connection with the origin of crystals may seem to 

 some people to be quite absurd, because they have 

 always been in the habit of believing that crystals 

 could, and do, habitually come into being de novo, with- 

 out the agency of pre-existing crystals. But in spite of 

 the fact, that the majority of people are quite content 

 to believe that crystals originate in obedience to purely 

 physical conditions, and independently of pre-existing 

 c crystalline force ;' still, facts somewhat similar to those 

 which are to be met with in connection with the sister 

 problem, have induced some chemists seriously to ques- 

 tion the possibility of the de novo origination of crystals 

 in some supersaturated solutions. In support of this 

 statement, I need only quote the following passage from 

 Watts's Dictionary of Chemistry 1 : c This sudden crystal- 

 lisation, if not produced by cold, appears to depend 

 essentially on contact of the solution with small, solid, 

 perhaps crystalline particles ; for it is not produced by 

 passing air previously purified by oil of vitriol through 

 the solution, or by agitation with a glass rod previously 

 purified from dust by ignition. According to Vlolette 

 and De Gernez^ the sudden crystallisation is in all cases 

 induced only by contact with a crystal of the same salt^ 

 possessing the same form and degree of hydration as 



1 Vol. v. p. 349. 



