150 
DR. P. F. FRANKLAND ON THE QUANTITATIVE ESTIMATION OF 
The one alternative suggested by Hesse as possibly accounting for the undoubtedly 
slower deposition of the mould germs is thus rendered untenable, since neither mould 
germs nor bacterial germs appear to be present in air as aggregates, but as isolated 
individuals, and some other explanation of this difference in their behaviour must 
therefore be resorted to. 
The advantages which appear to me to attach to the new method of quantitatively 
determining the micro-organisms of the air, which I have described in the preceding 
pages, may be briefly summarized as follows :— 
1. The method possesses all the well-recognised advantages pertaining to the use 
of a solid cultivating medium. 
2. The results, as tested by the comparison of parallel experiments, can lay claim to 
a high degree of quantitative accuracy. 
3. The results, as tested by control experiments, are not appreciably affected by 
aerial currents, which prove such a disturbing factor in the results obtained by some 
other methods. 
4. The collection of an adequate sample of air occupies a very short space of time, 
so that a much larger volume of air can be conveniently operated upon than is the 
case with Hesse’s method. Thus, whilst the aspiration of 10 litres of ah’ through 
Hesse’s apparatus takes about three-quarters of an hour, by the new method about 
48 litres can be drawn through the tube in the same time, whilst a better plan is to 
take .two tubes and alternately draw a definite volume of air through each, as by 
this means duplicate results are obtained. 
5. As the whole plug upon which the organisms from a given volume of air are 
deposited is submitted to cultivation without subdivision, no error is introduced 
through the multiplication of results obtained from aliquot parts, and all the great 
difficulties attending equal subdivision are avoided. 
6. The risk of aerial contamination in the process of flask-cultivation is practically 
nil. 
7. The apparatus required being very simple and highly portable, the method is 
admirably adapted for the performance of experiments at a distance from home and in 
the absence of special laboratory appliances. 
I must express my thanks to Me. Hart, A.R.S M., for the zeal and patience with 
which he has assisted me in this investigation. 
