468 FREDERICK KEEBLE. 
whilst those exposed to the light and supplied with uric acid 
were pale brown in colour, and were seen, on microscopic 
examination, to contain a very considerably larger number of 
intact yellow-brown cells. 
Another experiment was started on August 28th with 
three similar lots of animals. These lots may be designated 
‘filtered, light,” “filtered, light, uric,” and “ filtered, dark.” 
After twenty-one days (September 18th) the reductions in 
size of the animals and in the numbers of their yellow-brown 
cells were very great in the “filtered, dark,’ and least in the ~ 
“filtered, light, uric.” The measurements of animals taken 
as samples were—‘ filtered, dark’? 55 x 20 divisions (oc. 
micrometer, L. 2. 3); “filtered, hight, uric” 90 x 40. That 
is the animals in the hight with uric acid were more than 
three times as large as those in filtered water in the dark. 
The experiment was continued. During the following 
weeks the “filtered, dark” and “filtered, light” animals 
dwindled, lost all their yellow-brown cells, became of micro- 
scopic size, and finally died. On October 21st specimens in 
“filtered, light, uric” were still alive, of recognisably brown . 
colour, and possessed of many normal, yellow-brown cells. 
Finally, on October 28th a “filtered, light, uric”? specimen 
was still alive, and, though reduced considerably in size, was 
rich in yellow-brown cells showing no sign of degeneration 
or of digestion. 
When it is remembered that the animals were kept in 
limited supplies of sea-water only occasionally renewed, and 
that, during the time of the experiment, they were brought 
from Brittany to Reading, the effect of the uric acid in main- 
taining the yellow-brown cells and the animals alive for the 
space of two months will appear the more remarkable. From 
the experiment it is clear that the yellow-brown cells utilise 
uric acid as a source of nitrogen. It follows also that when 
the conditions admit of photosynthesis and when uric acid is 
supplied as a source of nitrogen the yellow-brown cells not 
only maintain their own existence, but also that of the animal. 
That the algal cells may contribute not only fatty but also 
