STREAM POLLUTION 
401 
In the weaker concentrations of such effluents and harmful substances, the precipitate 
coated the gill filaments and filled the filament interspaces so that the water pumped 
through the mouth and onto the gills for the aeration of the blood could not reach 
the cells of the gill filaments. Consequently, the aeration of the blood with its accom- 
panying gas exchanges was prevented, and sooner or later death followed from a 
combination of anoxemia and carbon-dioxide retention. 
If still larger masses of flocculent precipitate were formed, as was the case when 
the stronger effluents were tested, the interlamellar spaces were clogged and move- 
ment of gill filaments became impossible. This condition affected the circulation of 
the blood in the gills, in that stasis of the blood in the gill capillaries usually follows 
cessation of movement of gill filaments in a short time. Kolff (1908) in her studies 
of fish hearts found that the pulsation of the heart is only one of the forces necessary 
to drive the blood through the gill capillaries, and that the movements of the gills 
are important in maintaining the gill capillary circulation. 
If the scales be removed from the midventral portion of the precardial region of 
a pithed goldfish and a tiny steel needle (the minuten nadeln on which entomologists 
mount very small insects) be forced through the body wall and into the pericardial 
cavity, when proper adjustment is made, this needle, if examined under a binocular 
microscope, can be seen to swing with each heart beat. Using this procedure the 
rate of the uninjured and unexposed heart in situ can be recorded for hours. Such 
fish, when the gills were perfused via the mouth with water containing salts of heavy 
metals or other substances producing these heavy mucoid precipitates, continued 
their normal respiratory movements and heart action until the precipitate clogged 
the gills and mechanically prevented the movement of the gill filaments. At that 
time an abrupt change in the activities of the heart was usually noted, the heart 
action dropping to about one-half its former rate. Heart block also often developed 
at this time. When these changes in heart rate and heart action were noted, the 
gill capillaries were always found to be gorged with blood on the efferent or cardiac 
side and showed practically complete to complete stasis of the blood in the capillaries. 
This same condition of blood stasis in the gill capillaries was noted in other fish in 
which anoxemia was produced by exposure to water containing little or no dissolved 
oxygen shortly after cessation of respiratory movements, so that the importance of 
the respiratory movements for the maintenance of capillary circulation in the gills 
was well established. After its rate had dropped to approximately one-half normal, 
the heart continued to beat for hours (in some cases for over 24 hours), although the 
circulation through the gills was completely blocked. In fishes which had ceased to 
make movements of any sort, either respiratory or general, after prolonged exposure 
to water low in dissolved oxygen, the hearts were found to be beating even when 
these fishes were opened under oil to exclude even momentary aeration of the peri- 
cardial fluid. 
The various substances producing these heavy precipitates, as well as many 
other pollutants (acetic acid, volatile extracts of crude oil, and others) which did 
not form precipitates with mucous secretions on the gills, also produce death by 
asphyxia through direct damage to the gill filament cells, which in turn cause stasis 
of the blood in the gill capillaries. Death from anoxemia and circulatory failure in 
the gills, therefore, was regularly found in fishes dying either in waters containing 
