[3] BIOLOGY OF THE RHINE SALMON, 429 
opinion by the examination of a number of intestines, and, in view of 
the enormous increase in the size of the ovaria, he reaches the conclu- 
sion that the winter and spring salmon and the spawning salmon do not 
belong to the same immigration. The stay in the Rhine of both kinds 
is much shorter than had been supposed hitherto. Immature salmon 
come and go, and are finally replaced by almost mature salmon, which 
ascend the river direct from the sea. 
For my own part I feel that, after having for 4 years examined the 
intestines of Rhine salmon of both sexes, at all seasons of the year, I 
cannot but agree with the opinion expressed above, that the Rhine 
salmon, from the time it ascends the river from the sea until it has finished 
spawning, never takes food, and that, as a rule, it does not take any food 
afterwards. Even in winter and spring-salmon from Holland I have thus 
far looked in vain for any remnants of food. In comparison with the 
wide stomachs of the salmon from the Baltic and the North Sea, which 
had thin walls and were generally stuffed with fish almost to repletion, 
the Kralingen (Dutch) salmon had universally a contracted cesophagus, 
and the walls of their stomachs were laid in folds; the opening was 
very narrow; the appendages, not taking into consideration the con- 
tents and the layers of fat, were likewise thinner and not nearly as large 
as in the sea salmon. Occasionally I found a small stone, a piece of a 
blade of grass, or a stalk of some plant, which had entered with the 
river water and had been swallowed. Once I found in the small intes- 
tines a tolerably large larva of an insect, but entirely undigested and 
intact. Of secretion I found in the intestines proper sometimes a small, 
and at other times a large, quantity of slime, of more or less bilious 
color, although the gall-bladder was invariably empty. The bile, there- 
fore, seems to flow from the liver direct into the intestines. The cesopha- 
gus and stomach did not, in most cases, contain anything, at least noth- 
ing but a faint trace of a sticky and almost transparent slime, which 
was only occasionally more plentiful and somewhat thinner, but never 
acid. The duodenum, with its appendages, occasionally (but not always), 
more especially in very flat fish which had recently come from the sea, 
contained a more plentiful secretion in the shape of a sticky, slimy mass, 
which, by numerous detached epithelium cells, had become turbid, and 
somewhat resembled pus. But in no case did I find traces of digestion, 
of a softening and dissolving influence on the walls of the stomach and 
the intestines, of these secretions. Although the glycerine extract from 
this pus-like substance, when dissolved in diluted hydrochloric acid, 
occasionally dissolved fibrous matter to a small extent, it must be said 
that, with the exception of the bile, no effective gastric juice is secreted. 
It is, moreover, worthy of note, that even in the Aralingen (Nether- 
lands) salmon there is no tendency whatever to early putrefaction, such 
as is found in the intestines of every animal which, with its food, intro- 
duces from outside germs of putrefaction. This seems to indicate that 
