Judmj—Lakes in Central America. 
235 
along this portion. Also the volume of the water discharged 
through the outlet stream does not seem to indicate that the lake 
receives an unusually large amount of spring water. As noted 
above, the water of the thermal spring at lake Atitlan possessed 
a high degree of acidity and, since lake Ilopango is situated in 
a region that is affected by volcanic disturbances, it seems more 
probable that the acidity of its water is mainly of volcanic origin 
rather than derived from the usual sources noted above. 
Lake Amatitlan had the smallest amount of fixed carbon 
dioxide with 32.28 cc. per liter of water and Atitlan came next 
in order with 37.84 cc. (See table II, p. 244.) The other two 
lakes had distinctly larger amounts, Ilopango having an aver¬ 
age of about 48 cc. and Coatepeque about 56 cc. It will be 
noted that all of these tropical lakes possessed a distinctly 
larger amount of fixed carbon dioxide than Cayuga and Seneca 
lakes in the state of New York. In fact Ilopango and Coate¬ 
peque contained more than twice as much as these temperate 
lakes. 
With respect to the amount of this gas these four Central 
American lakes belong to the same class as the majority of the 
lakes in southeastern Wisconsin. In this quarter of the state 
the waters of most of the lakes that have been tested so far, 
possess between 30 cc. and 45 cc. of fixed carbon dioxide per 
liter. Only one of these lakes, however, reaches an average of 
48 cc. to 50 cc. Toward the end of the summer period of stag¬ 
nation the bottom water in some of these temperate lakes con¬ 
tains a larger amount of fixed carbon dioxide, but this is found 
only in lakes where the bottom water becomes highly charged 
with free carbon dioxide. This highly carbonated water acts 
upon the comparatively insoluble normal carbonates in the 
bottom mud and converts them into the readily soluble bicar¬ 
bonates. The maximum amount of fixed carbon dioxide that 
has been found in the bottom water of any of the Wisconsin lakes 
was found in Garvin lake on two different dates in 1909. It 
amounted to 63.2 cc. but the surface water on these dates con¬ 
tained respectively 35.9 cc. and 34.7 cc. 
The Net Plankton. 
Plankton catches were made in each of these four tropical 
lakes at the same time that samples of water were obtained for 
the chemical tests. They were taken with a vertical closing 
