198 THE EVOLUTION OF LIFE 
change of this kind is also often late in manifesting 
itself. 
(4) The fluid itself may remain perfectly clear ; 
but at the sides of the vessel, or on some phosphatic 
sediment at the bottom, one, two, three, or more 
little whitish tufts may show themselves, which 
continue to increase in size for two or three days, 
the fluid itself still remaining perfectly clear. These 
are not tufts of some fungus, as might be thought 
from their appearance, but are tangled masses of 
long Bacilli-filaments.! 
(c) In other cases the fluid itself may remain clear, 
and no tufts may show themselves; but slowly, and 
after many days, more or less of a flocculent 
sediment accumulates at the bottom of the vessel in 
which organisms are to be found. This latter kind of 
change has not been much considered in this paper ;? 
it is one which has only shown itself on a few occa- 
sions, and is, moreover, one which, judging from my 
1 Sometimes they have more the appearance of what Professor Cohn 
describes as V2br70 serfens (‘ Beit. zur Biolog. der Pflanz.,” Bd. 1. Heft 2, 
Taf. iii. fig. 18). But I entirely disbelieve in the propriety of regarding 
such differences as he distinguishes between these forms as having any 
specific or even generic value. Dr Warming, of Copenhagen, says: 
“Les Bactéries sont douées, en réalité, @une plasticité tllimitée, et je 
crois quwil faudra renoncer au systeme de M. Cohn et de quelques 
autres savants qui caractérisent les genres et les especes d’apres leur 
forme.” Quoted in Quart. Journ. of Microsc. Sci., Jan. 1877, p. 85. 
It is, however, only fair to add that Professor Cohn was himself by no 
means free from doubt on this subject. 
2 This is a kind of change which I have spoken of as “smouldering 
fermentation.” In the latter portion of a paper in the Proceedings of 
the Royal Soctety, No. 145, 1873, 1 have fully described the different 
degrees of fermentability apt to be shown by various kinds of 
fluids when, heated to different degrees, or when, after the heating, 
they are subsequently exposed to different incubating temperatures. 

