THE MICRO-ORGANISMS PRESENT IN THE ATMOSPHERE. 
127 
Colonies obtained from 1 c.e. 
of water. 
I. 
II. 
Chelsea, Sept. 1886 . 
West Middlesex. 
83 
31 
90 
23 
Southwark. 
56 
42 
Grand Junction. 
18 
16 
Lambeth. 
61 
57 
New River. 
• 19 
15 
River Thames at Hampton. 
8,300 
8,500 
River Lea. 
3,500 
4,000 
Now many of the discrepancies observed between similar plates prepared from the 
air plugs are largely in excess of anything observed in the case of these ordinary 
water plates, and it is obvious that when these discrepancies have been multiplied by 
10 or by 20, as is the case, the result is still less satisfactory. 
This objection applies, as already pointed out, in a still greater degree to Miquel’s 
process, since the latter is based entirely upon the assumption that such homogeneity 
is obtained in the aqueous emulsion of the plug. 
In order to overcome all the difficulties to which reference has been made, I have 
devised the following process, which I will now describe in detail. 
1. Construction of Tubes and Plugs .— The tubes through which the air under 
examination is aspirated are about 5 inches in length and \ inch internal diameter. 
Fig. 1. 
a he 
The front end (A) of the tube is open, the other extremity (B) being slightly con¬ 
stricted. At a distance of 1 inch from the extremity (A) the tube is constricted so as 
to form a support for the first plug (a), which is placed just in front of the constric¬ 
tion. At a distance of 2^ inches from the plug (a) the tube is again constricted to 
form a support for the second plug (b), whilst resting against the constricted extremity 
(B) there is a third plug (c). 
In constricting the tube, the extremity (B) is first constricted and the plug (c) 
introduced at (A), and pushed down to (B); the tube is next constricted at ( b ), and 
the second plug introduced and put in position there, whilst finally the tube is further 
constricted at (a), and the plug (a) introduced. Plug (a) is invariably made more 
pervious than ( b ), so that any organisms which may be carried by the current of air 
through (a) may find a greater resistance in ( b ), and thus, if ( b ) is found to be 
altogether free from organisms, it clearly shows that they must have all been arrested 
by (a). 
