necessary to kill Bacteria, Vibriones, §c. 



333 



highest to the very lowest degrees of ferinentability. These gradations 

 are dependent principally upon the nature of the fluids or mixtures em- 

 ployed, and upon the degree of heat to which they have been submitted, 

 though partly also to the temperature, pressure, presence or absence of 

 filtered air, and degree of light to which the mixtures are subsequently 

 exposed. For the sake of convenience, these gradations may be ranged 

 into several distinct groups, though of course any such divisions as I am 

 now about to sketch are purely artificial and are connected with one 

 another in nature by innumerable transitions. 



Nature of Fluids. 



A. Turnip -infusion with cheese, turnip- 

 infusion neutralized by liquor potassa?, 

 ordinary turnip-infusion, strong hay-in- 

 fusion, &c. 



B. Turnip-infusion neutralized by liquor 

 potasste, ordinary turnip -infusion, ordi- 

 nary hay -infusion, &c. 



C. Beer- wort*, &c. 



D. Weak hay- infusions, urine, solu- 

 tions containing amnionic carbonate and 

 sodic phosphate with minute organic im- 

 purities, &c. 



E. Weak hay -infusions, urine, solutions 

 containing ammonio-citrate of iron and 

 minute organic impurities t, &c. 



F. Solutions of amnionic tartrate and 

 sodic phosphate with minute organic im- 

 purities, &c. 



Nature of Eesults. 



Within two to four days marked turbidity, 

 owing to the appearance of swarms of 

 Bacteria and Vibriones. Fluids more 

 or less foetid. {'Putrefaction.') 



No uniform turbidity, but growth of fioc- 

 culi in a more or less clear liquid. After 

 a time the fiocculi (composed of aggre- 

 gated Bacteria and Vibriones) gradually 

 subside, and the activity of the process 

 ceases. Fluids either foetid or having a 

 mere sour odour. 



Fluids which become more or less uni- 

 formly and rapidly turbid, owing to the 

 appearance of swarms of Torulce. 



Do not become visibly turbid or produce 

 visible fiocculi, although on microsco- 

 pical examination they may be found to 

 contain living Bacteria pretty uniformly 

 distributed, but in comparatively small 

 quantities. The odour is often not 

 more appreciably altered than the clear- 

 ness of such solutions. 



Same as in the last group J, though after 

 weeks or months a dirty-looking sedi- 

 mentary matter slowly accumulates at 

 the bottom of the flask, which on mi- 

 croscopical examination is found to be 

 composed partly of Bacteria with Vi- 

 briones and Leptotlirix, and partly of 

 Torulce or more thick-walled fungus- 

 germs. 



Same as in the last group, only the dirty 

 sedimentary matter which accumulates 

 never contains either Bacteria, Vibriones, 

 or Leptothrix. Living Torulce and 

 thick- walled fungus-germs in various 

 stages of formation are frequently met 

 with, and also, occasionally, a mycelium 

 resulting from the development of some 

 of these bodies. 



* I have had no experience with such a fluid myself. M. Pouchet's observations 

 were, however, most striking on this subject (see his ' Nouvelles Experiences,' Paris, 

 1864, p. 190). 



t In solutions containing iron, green organisms may subsequently be found (see 

 ' Beginnings of Life,' vol. ii. p. 157). 



\ This, in fact, is in many cases the kind of change which the fluids last described 

 ultimately undergo. 



