ON SEWAGE AND PARASITES, ETC. 359 
that would, I reckon, only give us an average of one egg in 
seven ounces of sewage. Let those, therefore, who demand 
microscopic evidence as to the existence of entozoal germs 
in sewage, consider the amount of skill, time, and patience 
requisite for the detection of the presence of an organic par- 
ticle, having a diameter of -g-f-o-th of an inch, and being con- 
cealed in such a relatively huge mass of offensive material. 
Into this question of dispersion I cannot at present go 
further; besides, it must be obvious that the consideration of 
the vitality of the eggs of parasites, under varying conditions, 
is the point to which our attention should be primarily di- 
rected. Now, although, as far as I am aware, no investiga- 
tions on this head have ever been made with especial refer- 
ence to the sewage question, we are by no means destitute of 
facts of the highest practical value in this relation. My only 
regret is that the facts 1 have now to bring forward must be 
presented in so restricted and crude a shape. At all events, 
sufficient will be said to show the fallacy of drawing general 
conclusions from isolated data. 
j Bilharzia Hamatobia . — Whilst the eggs of this entozoon 
are still in the urine, there appears to be neither the power nor 
the inclination on the part of the embryo to escape from its 
shell ; yet from the moment when the eggs are removed from 
the urine and placed in water, a series of changes are com- 
menced and carried on with extraordinary rapidity. In less 
than two minutes I have seen a hitherto motionless embry- 
onic mass alter its form, become violently agitated, and burst 
out of its envelope in the condition of a free swimming ani- 
malcule. Commonly, more time is required, especially if 
any appreciable quantity of urine is allowed to remain in the 
new medium. Thus, to record only one observation : — On 
August 21st last I placed a drop of fresh urine, containing 
twelve eggs of Bilharzia , on a slide under the field of a one- 
inch objective glass ; and to this I added about eight drops 
of drinking-water. The first embryo escaped at the expira- 
tion of seventeen minutes, whilst two more emerged in ano- 
ther minute ; the fourth embryo appeared at the end of the 
twenty-sixth minute, the fifth in twenty-eight, the sixth in 
thirty-two, the seventh in thirty-four, the eighth in thirty-seven, 
the ninth in thirty-eight, the tenth in forty, the eleventh in 
forty-three, and the twelfth in forty-six minutes respectively. 
{To be continued .) 
