(418) 
importance for the digestion. Moreover, in consequence of the results 
obtained by painstaking and interesting experiments on animals, 
bred sterile from their birth, the influence of the intestinal bacteria 
on digestion, has been denied by some (NUTTALL and THIERFELDER), 
confirmed by later researches (SCHOTTELIUS). 
The foundation of these numerous investigations, the determination 
of the number of bacteria in the different parts of the intestinal 
canal, must be called an erroneous one, in as much as all these experi- 
ments relate only to the living bacteria present in the intestinal 
canal. And as little as the sanitary condition of a population can 
be judged only after the number of living individuals present at a 
given moment, or the murderousness of a battle exclusively after 
the number of remaining soldiers, without taking into consideration 
the killed, as little is a right insight to be acquired into the sanitary 
condition of the bacterial population of the intestinal canal and the 
battles fought there between these lower beings and the living 
animal organism (anti-bacterial influences), by only looking at the 
living individuals, leaving the dead ones out of account. 
The proportion existing between the number of living and of 
dead individuals I call the sterclity-index; this proportion thus 
indicates the degree of sterility reached by a determined population 
of bacteria. 
The sterility-index of a bacterial population is estimated from 
the relation of two data: 1%* The difference in number of this 
population found between the culture-method and the microscopic 
counting-method (proportional number), and, 2"¢ the determination 
of that fraction of the microscopically counted organisms, which 
are still able to propagate. 
The latter determination is effected biologically : the living organisms 
in the bacterial population are allowed to propagate and after a 
certain time the number is again determined, as well microscopically 
as by culture. In order to accomplish this propagation the same 
medium is by preference used in which the original bacterial popula- 
tion developed, as the lower organisms also have in the beginning been 
able to increase in this medium. Only it will be necessary by dilution 
sufficiently to remove an eventually active anti-bacterial action, 
which originates from the fluids of the human or animal body. The 
moment for the second determination should in each special case be 
fixed experimentally. The difference in time must not be too short, 
else the increase of living organisms is too slight to produce a 
distinct augmentation of the number of micruscopically counted 
