22 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
and it yields mechanical surface aggregates such as are 
obtained from pure soap solution instead of solid saponin. 
The practical importance of such preferential adsorption les 
in the lessons it teaches as to the necessity of— 
(1) strictest cleanliness in studying adsorption 
phenomena ; | 
(2) bearing in mind its possibilities when dealing 
with complex biological liquids such as blood-serum. 
Imagine, for example, a serum with much of a less 
adsorbable substance and very little .of a more 
adsorbable one—the first rapid adsorption would be of 
the less adsorbable though more plentiful substance, 
but given time enough for the other to get to the 
surface this might eventually entirely displace the first- 
arrived—provided the two rivals did not enter into 
some combination or suffer a chemical change under 
surface catalytic influence. 
FLOATING ANIMALS. 
A brief explanation may here be given of the way in 
which the contractile pull of a water-air surface is exploited 
by various small aquatic animals, and serves to support 
them near the surface, even though they are heavier than 
water. ‘Thus the small black hairy insect Podura frisks 
about on the surface of a pond like a fly on quicksilver ; 
the larvee of the gnat hang head downwards suspended from 
the water surface by means of their breathing tubes, much 
as a ham hangs from a hook in the ceiling; numerous 
Entomostraca which normally live in the water, when by 
any accident they get on to the surface are, according to 
Scourfield, apparently quite incapable of getting back and 
float helplessly on their flat sides until they starve to death 
or are blown ashore. For numerous other instances the 
fascinating writings of Professor Miall should be consulted. 
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