(419) 
bacteria; and, again, the quickness of increase of the living individuals 
corresponds with the nature of the food, the presence of anti-bacterial 
influences, etc. Nor must this period be taken too long because 
finally the dead individuals decompose and vanish. 
If the excess of microscopically counted bacteria prove to have 
completely died, the sterility-index is directly found by diminishing 
the original proportional number with 1; this is for instance the 
case in human faeces!). But when only a fraction died, so that 
part of the microscopically counted organisms are alive but do not 
develop on our usual culture-media, then, for the estimation of the 
sterility-index from the data found, it is admitted that the living 
but not cultivable individuals have multiplied during the period of 
observation in the same measure as the cultivable ones. 
The determination of the sterility-index might also directly be 
made microscopically, if the bacteria that have died already before, 
could be distinguished by microscopically perceptible changes from 
those organisms which in the beginning were alive. Indeed, after 
death there occur modifications in the bacterial bodies, at least in 
the intestinal canal of the rabbit, which considerably alter the 
pigment-absorbing faculty of these organisms. In general three 
stadia of decomposition may be distinguished: 
Ist. The granule-stadium, where one or two (seldom more) very 
darkly coloured granules may be observed in a for the rest lightly 
coloured stroma of the bacterial body ; 
2nd, The shade-stadium, the dark granules are no more present 
and the bacterial stroma is still lighter coloured; and 
3rd, The membrane-studium in which the bacterial stroma absorbs 
no pigment at all; at least there remains nothing but a fine coloured 
line, which still very markedly and sharply indicates the margin 
of the original organism. 
The greater part of these decomposing bacteria are so fragile that 
they can but be observed by the use of the delicate treatment of the 
„moist staining’; when applying Kocn’s staining-method they mostly 
fall asunder at the drying and flaming of the preparations and 
then form what has been by some described as bacterial detritus. 
These post-mortem bacterial phenomena cannot however at first 
be used for the determination of the index of sterility, as they do 
not appear directly, but only some time after the death of the 
1) See my Paper ,Bacteriological investigations of human faeces”, Proceedings 
Royal Acad. of Sciences, Amsterdam, Vol. IX, p. 57, 
