48 Proceedings of Royal Society of Edinburgh. [sess. 
tenacity. Hneppe, from the mere fact of its being a secondarily 
derived function, considers it of little value for classification, as all 
characters for this purpose should depend on primary powers of the 
protoplasm, which as such, are unchangeable. At the same time, 
the extreme convenience and value of the gelatine methods as 
a means of diagnosis cannot be overrated, although the result 
arrived at in this way should in every case be further tested by the 
appearance of the growth on potato and in milk. 
The varying power of resistance of the same microbe, which we 
have had so frequently to refer to, has a great practical interest in 
its relation to the most important application of bacteriology — the 
antiseptic system. Koch proposed anthrax as a standard by which 
we might compare the relative efficiency of different disinfecting 
agents. Great confusion has, however, arisen from this, as not only 
anthrax, but other organisms also, exhibit varying powers of resist- 
ance. In determining the absolute value of an antiseptic agent, 
those conditions which cause the powers of resistance of the organ- 
ism to vary must be most carefully considered. This is still more 
necessary at present in consequence of the search after specific * 
disinfectants. It has been found that each organism exhibits 
idiosyncrasies in relation to antiseptic agents, being exceptionally 
susceptible to one, and more than usually resistant to another. The 
object being to find that substance, or combination of substances, 
which acts most vigorously on the disease germ, and yet injures 
least of all the tissues, the confusion occasioned by the organism 
itself not being constant in its properties, can be readily understood. 
In such experiments even a difference in the age of the culture may 
cause a serious discrepancy in the results. Thus, if the organisms 
experimented with are a brood of very young cholera cells obtained 
by incubation for 18 to 24 hours at the temperature of the body, 
the action of the antiseptic is much more marked than on an older 
culture. This is probably to be ascribed to the organisms in this 
stage of development possessing a more permeable membrane. 
The nature of the medium appears also to exert a certain influence, 
as anthrax which has been grown on potato is slightly less resistant 
than that form other strata, as agar-agar. We have here again to 
consider the influence which the acidity of the medium exerts on 
* Hueppq, Berliner klin. Woch., Nos. 46 and 47, 1889. 
