THE APPLICATION OF QUANTITATIVE METHODS. 129 
Canal 
River. Canal. Ditch. Basin. Erith 
Cyclapsir.-.-.c0 GIO) 23. 25.4 «40,5301 - 2) SOL ee 
Daphnia. .:..:-2:. Ba tae! |, 3.0)! 12. ONE aed gg 9 
CY DES uate ae ZO! us TO,Gr <-s 330.0 i | Oey O 
FROEMEISS ssc. see LOM eal, edivels ~ , sOllten, | a ane ee nmmnnSS 
PrncClidSa acer wet ON sa TO... «4cO02.. g, 4 
After September 2,— Ponds 
PV ClODS scam asec BOors, GiO- deny 26: 2-25.. (G.0r ace OG: 
Daphwia....65 x «- SO} ee Esha 8 es See Aeon ene 
Cy BEIS adele ta hhe ose TiO} tis) S-QAO, et (OO 2) WOl Fees meee 
OMCs taces7055.% LG) seh) w Slave ON so OnOuas paige 
Arimaeltds: (GLC... ful. Za ledv SocO) gee EsGhyee = thee eee 
The large number of Cyclops in the Thames, as shown in the 
first table, is probably due to the food supplied in the sewage. 
He had kept Cyclops on sewage matter since last May. If kept in 
clear water they died in a week. The average number of the ex- 
crements of these Entomostraca held in suspension at half-ebb tide 
at Erith is 170,000 per gallon. By calculating the different per 
centages of the several objects, they would perceive at a glance the 
change produced by altered conditions. Taking the Thames as an 
example, they would find that although there was a considerable 
reduction, there was no change in relationship until we came to 
the salter water at Gravesend. He was in hopes that by the study 
of this question it might be possible to utilize this method as a 
means of testing how far certain waters were or were not fit for 
drinking purposes, and also to form some judgment with regard to 
impurities discharged into rivers. He found that Cyclops was 
killed when it reached salt water, and he thought it would be inte- 
resting if they could form some estimate of the number destroyed 
in this manner. Engineers had kindly supplied him with data, 
and he had calculated the quantity of organisms destroyed per day 
by two different methods, and it was remarkable how nearly they 
agreed. Without going fully into particulars, the conclusion he 
came to was that at the end of May or the beginning of June the 
number of these Entomostraca killed by salt water was about 2600 
millions per day. 
Having exhibited on the screen drawings of the animals 
found, and described their general character, he gave a few de- 
tails as to the numbers found per nine gallons of water in various 
localities :— 
Swail. Swin. Pont. Colne. Screws. Stones. 
Ascidians...... RAD. So BUR FARO) EA Ae 
Annelids....... 9:20 ip REL Ol. Sah Re ey Ome Oo 
Rotifersts/:. 3) Ags eid 1S te eoul el Garten Sas Te 
Gammerds.oisi/>! Biay bee va Moy Nae st OA 
