192 HETEROGENETIC CHANGES IN 



Amoebae. This was the only kind of change seen, and is well shown 

 in different stages in Fig. 23 (x 500), together with some of the 

 unchanged masses below and to the left. 



For some reason these colourless units, exactly similar in appear- 

 ance to those of Fig. 20 which straightway developed into active 

 Monads, remained without further change during the fifth, sixth, 

 and seventh days ; then, on the eighth day, in a few of these masses 

 the colourless units were seen to be developing into brown Fungus- 

 germs, while, on the ninth day, very many of them were undergoing 

 this change — and still not a single Monad or Amoebas was to be 

 found. It looks, therefore, as if some change in the chemical con- 

 stitution of the fluid prevented the development of the segments 

 into Monads or Amoebae (as is so common during the third or 

 fourth days), and yet after a time favoured their development into 

 brown Fungus-germs. 



(3) On the Production in and from the Pellicle of discrete Corpuscles 

 which speedily develop into Flagellate Monads, or Amcebce, or else into 

 Fungus-germs. At the expiration of three or four days, according 

 as the temperature to which the infusion is being exposed is up 

 to, or some degrees below, 70° F., the first indication of the 

 formation of discrete corpuscles may be found. When a portion 

 of the pellicle has been taken up on the tip of a sterilised scalpel, 

 and rotated off on to a drop of water or of some staining fluid 

 placed on a microscope slip, and when the cover-glass has been 

 applied, we find on examination a thin membranous, granular- 

 looking layer surrounded by myriads of free and active Bacteria — 

 though no free Monads or Amoebae are to be seen. This layer will 

 probably be already flecked by many of the minute Zoogloea 

 masses already described ; but on examination with a power of four 

 or five hundred diameters portions of the pellicle lying between 

 them may be seen to display a more or less evenly granular appear- 

 ance, owing to the Bacteria, entering into its formation, having in 

 part ranged themselves at right angles to the surface of the fluid, 

 and being motionless by reason of being imbedded in the viscid 

 gloeal material which they have excreted.' In many other places, 

 however, especially when the pellicle is looked at slightly above 



' Though motionless, they are far from being dead as Pouchet imagined. He 

 said (" Heterogenie," 1859, p. 354) : " La pellicula proligere etant constamment 

 formee par les cadavres des animalcules dont les generations se sont succede," 

 He, in fact, invariably spoke of the Bacteria in the pellicle as "les cadavres." 



