294 THE BEGINNINGS OF LIFE. 



examination of the solutions themselves in which the 

 plastide-particles, and the Bacteria or Torul*, appear. 

 The mode in which they make their appearance was 

 first studied by Mantegazza 1 , though others have sub- 

 sequently made similar observations. I have frequently 

 watched their appearance, during warm weather, in 

 portions of organic solutions hermetically sealed in 

 small glass tubes, or, more advantageously still, in thin 

 films of fluid beneath a covering glass, after it had been 

 cemented 2 to the glass slip, or after the fluid had been 

 otherwise prevented from undergoing rapid evaporation. 

 If a drop of a very strong infusion of turnip 3 be 

 taken (after it has been filtered five or six times 

 through the finest filtering paper), and mounted in the 



1 Professor Mantegazza first watched the appearance of Bacteria in 

 a solution containing some fragments of vegetable tissue, enclosed in a 

 hermetically-sealed glass tube. On this occasion he watched the 

 solution assiduously for sixteen consecutive hours. At the expiration 

 of two hours, he saw the first particles appear in the solution, at first 

 simply exhibiting a slow, oscillating movement, but, after a time, darting 

 about with the rapid movements by which active Bacteria are cha- 

 racterized. Their number increased imperceptibly, till, at the end of ten 

 hours, the liquid had become quite cloudy. (See ' Giornal. dell. R. Isti- 

 tuto Lombardo,' t. iii. 1851.) 



2 Taking care to employ a cement which has been previously ascer- 

 tained not to be hurtful to Bacteria, and to leave a minute aperture at the 

 circumference of the glass uncovered by the cement. Or a drop of the 

 fluid to be examined may be placed in an ordinary animalcule cage, and 

 the cover then pressed down so as to flatten the drop into a thin film. 



8 This I have found to answer best. The water of the infusion should 

 not at any time be hotter than about 35 F. Sometimes the appearance 

 of Bacteria has been hastened by neutralizing the natural acidity of the 

 infusion by liquid potassse. 



