too much confidence as he was wont to use a cooling bath of —12°*). 
Neither could he apply the later published correction of BRCKMANN. 
With Chelone imbricata L. (sea-turtle) he found —O’.61 and —0°.62. 
Roper?) found in a Ganoid (sturgeon?) A = 0.76, in Lophius 
piscatorius L. O°.68 and 0°.80, in Orthagoriscus mola I. 0°.80, in 
the sea-turtle Phalassochelys corticata Rondelet 0°.602 and in a 
mammal, living in the sea, the grampus Phocaena communis Less 0°.74. 
The numbers obtained for the blood of the eel Anguilla vulgaris 
Flemm. are very remarkable. With vigorous specimens I found 
formerly at Leyden — 0.773°, at Bergen — 0.653°, at Utrecht 
— 0.587°. Now the eel belongs to a family of tropical sea-fish ; 
most species occur in the Dutch Indian Archipelago, they often go 
into brackish water, others are deep-sea animals. Our common eel 
excellently bears quick variations of the percentage of salt. Born in 
the sea, it enters the river mouths as a young animal and remains 
in fresh water until the time of propagation approaches. The eel 
which is caught in the fresh or somewhat brackish waters of Frisia, 
is put at Workum into caufs into which the seawater has free 
entrance, goes to London and is sold on the Thames from these 
caufs. The layer of slime, with which their skin is covered facilitates 
this transition. Pavun Burr*) noticed that all the eels which he put 
from the fresh water into the seawater himself, supported the sudden 
change, whereas those which his assistant handled, all died. He used 
a little net, whereas the assistant took them with his hand, held 
them in a rough towel and in this way removed the layer of slime. 
The eel shows in its osmotic pressure sometimes the type of a 
seafish, sometimes it approaches that of a freshwater fish. The high 
P, with the trout, as an original migratory fish, now also becomes 
to some extent explainable. 
Here a field of study lies open which may be urgently commended 
to the Committee for the international investigation of the sea. 
How do the marine bony fishes maintain in their blood a so 
much lower osmotic pressure than exists in the seawater? Some 
observations on the urine of the cod, sea-wolf and G. virens can 
perhaps throw some light on this question. The 4 of the urine was 
always lower, the osmotic pressure less than that of the blood. 
1) G. Fano et F. Borrazzr, Sur la pression osmotique du serum en différentes 
conditions de l’organisme. Arch. ital. de biol. 26, p. 46, 1896. See especially p. 47. 
2) Hampurcer |. c. I. p. 466. The original article of Ropier in Travaux des 
laboratoires d. 1. soc. sc. et station zoolog. d'Arcachon. 1899. p. 103, I have not 
at my disposal. 
3) P. Reanarp, La vie dans les eaux. p. 438. Paris. 1891, 
