Still another unknown feature of avian botulism concerns toxin distribution on 
mud flats. Some investigators believe that danger areas are restricted largely to 
marginal zones favorable to toxin production or concentration. Others hold to the 
view that the toxin is scattered widely, and possibly irregularly, in the form of 
tmicrodoses." Neither concept seems to be supported by conclusive evidence. 
The question has been raised whether toxic material is produced with great 
rapidity after reflooding of previously partially dried lake-bottom soils, whether 
jt is concentrated there by physical action of climatic factors associated with 
reflooding, or whether it is formed gradually by bacteria during the drying period 
and then released in quantity by chemical or physical action following the re- 
flooding. Some indications are available on several sides of this question. In 
recent laboratory tests, toxin of considerable potency was formed in inoculated 
bacterial medium within a period of a few hours. At the same time, some field 
studies seem to indicate that storage and release of toxin may occur. Rapidity 
of development of mortality waves after a reflood appear to reflect a sudden re- 
lease to ducks of vast amounts of toxin. Well-authenticated occurence of late fall 
and early spring outbreaks of avian botulism in ducks, sometimes during icy condi- 
tions in the marshes, is difficult to explain in any other way than by storage and 
later release. 
In naturally intoxicated birds, the time between pick-up of toxin and develop- 
ment of marked symptoms seems to be shorter than that seen in the laboratory with a 
similar slightly less than lethal dose. By the best available field estimates, the 
ghortest time lag between natural pick-up of toxin by birds in their feeding activity 
and development of heavily disabling symptoms is about 18 hours. In laboratory work, 
a slightly less than lethal dose of toxin has resulted in prostration at a minimum 
of perhaps 28 hours. The mechanisms behind this observed phenomenon are unknown, 
like those in other problems discussed above. 
It is to be hoped that investigative programs now under way and those that may 
come in the future will answer some of the present unknowns. Then it may become 
possible to control more effectively this great natural scourge of western waterfowl. 
Cooperation by all those concerned may make this possible. 
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