128 THE MICROSCOPICAL NEWS. 
had been applied to physics and chemistry, but hitherto almost 
insuperable difficulties had prevented their application in the case of 
biological questions. He proposed to show that it was possible to 
deal with certain matters in this manner. Possibly his training had 
to some extent led him to carry out these investigations. About 
two years ago he was requested to undertake a long series of in- 
vestigations with respect to the matters held in suspension in the 
water of the river Thames in order to give evidence before a Royal 
Commission appointed to report upon the question, and in order to 
do the work effectually, he lived for three months on the Thames 
in his own yacht. As the result of his various researches, he had come 
to the conclusion that the removal of impure matter discharged into 
our rivers by sewers was by no means a chemical question, as was 
generally supposed, but to a large extent a biological one. He 
found that these impurities formed the food for some of the minute 
living organisms which swam in the water. He then considered it 
most important to decide the number of these minute creatures 
per gallon of water, and devised a method which he believed had 
not been tried before. The course he adopted was to pass nine 
gallons of river water through a very fine wire gauze sieve of about 
120 meshes to the inch, and all the minute creatures upwards of 
soo Of an inch in diameter remained. ‘The sieve was then washed 
out with clean water; the objects counted in a glass trough which 
was repeatedly filled. The counting was facilitated by the different 
ways in which the objects moved about in the water, which enabled 
him the more readily to distinguish them. In addition to the 
small adult animals there were the larve of larger ones. He was 
surprised to find such a large number of animals he did not expect 
to meet with. He took with him various poisons for the purpose 
of killing the objects, but he found a more simple method was to 
add a little alcohol, and after pouring off the salt water, to place 
them in rain water to which an equal measure of alcohol had been 
added, which prevents the precipitation of sulphate of lime. After 
pouring this off, the specimens were kept in alcohol. 
The following tables were thrown on the screen by means of the 
oxyhydrogen lantern :— 
FRESH WATER RESEARCHES, 
NUMBER PER NINE GALLONS OF WATER. 
Pure River. Thames. Impure River. 
Cyclops... ae 4.1 aa 26.3 Bh 1.5 
Daphnia.. a 2.0 we “9 ae 1.2 
CYP S..ciss es Li eh ) tik fo) 
Annelida.. = 1.4 ae 4 ee) ECTS 
Table showing the number of objects per nine gallons of water 
taken from different localities, chiefly near Maldon, Essex :— 
