THE SPEED OF MIGRATION OF SALMON 
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tions. This tremendous output of energy can only take place 
at the expense of nutritive substance on hand when the journey 
is begun. 
A still more fundamental process is occurring during the mi- 
gration, namely, the rapid development of the reproductive tis- 
sues. When the salmon enter the mouths of the rivers, especially 
earlier in the season, the reproductive organs are very small in 
size and immature in development. As the journey progresses 
the reproductive organs in both sexes grow rapidly and the repro- 
ductive cells approach maturity of form and structure. This 
growth of new tissue in the absence of an income of food represents 
a remarkable physiological process. Such growth can take place 
only at the expense of materials on hand, and to produce new tis- 
sues requires substances more complex than the mere fats, which 
might possibly account for the production of the energy of motion. 
We have, therefore, in this animal two lines of physiological activity 
which lend peculiar interest to the subject of nutrition in the ab- 
sence of food, namely, first, the source of the dynamic energy 
expended by the animals, and second, the source and character 
of the nutritional changes which result from the development of 
a special set of organs at the expense of other portions of the body. 
It is obvious that the question of the rapidity and of the intensity 
of the energy changes in these processes are the all-important 
factors. In order to secure information which would help to eluci- 
date those factors, it became necessary to determine as accurately 
as possible the details of the migration of salmon. It seemed 
desirable to determine the speed of the migration, the total time 
consumed by the fish in the journey, and the detailed character 
of the migration, all with a view to determining the intensity 
of the energy put forth in making the journey. 
In order to subject the questions at issue to a test, I arranged a 
marking experiment on fish secured in the lower Columbia River. 
It seemed that the only way to get accurate information would 
be to mark individual fishes in such a way as to be absolutely cer- 
tain of their identification. My plan was to secure the live fishes, 
mark them with metal tags and turn them loose in the river again 
with the hope that they would be re-taken. The numerous com- 
