( 543 ) 
minated, by taking the blood in the morning before breakfast, only 
varies between 0.56 and 0.58. 
We can only to a limited extent imagine why the percentage of 
salt (for this is the chief point) of blood and lymph may only vary 
between narrow limits. The globulines require a certain concentration 
of “medium salts’ in order to remain in solution. If horse serum is 
diluted with 1°/, volume of distilled water, a precipitate is already 
formed, i.e. with a percentage of salt corresponding to A — 0.24. 
Why an increased percentage of salt should be tnjurious is less 
clear. Danger for precipitation of albumens would only occur with 
much higher concentrations, at any rate with horse serum. Yet the 
fact, found by Roprer’) that the blood and the somatic fluids 
(pericardial and peritoneal) of rays and sharks are isotonic with 
seawater but contain less salt, the deficiency being compensated by 
the retention of 2 to 2.7°/, of urea, points to a strong need of the 
organism of the Vertebrates to keep the percentage of salt below a 
certain value. Grijs ®) has found that blood-cells are permeable for 
urea so that this substance helps to bear the osmotic pressure against 
the seawater but discharges the celis of a third of 23 to 24 atmos- 
pheres. I have proposed le. to call this power of being isotonic 
with respect to seawater but of taking away from the cells them- 
selves part of the osmotic pressure “metisotony’’. 
The blood of Teleosteans has a freezing point which differs considerably 
from that of the seawater, in which they live. They possess ideotony 
but the individual differences are greater than have been remarked 
with the remaining veriebrates, so that it appears that they only 
imperfectly possess the faculty of rendering their P, independent 
of the surrounding medium. Before the figures are given, a summary 
of A and P, of different seawaters may be inserted. The numbers 
have been taken from M. Kyupsen’s Hydrographische Tabellen, from 
Prrrerson’s Review of Swedish hydrographical research in the Baltic 
and North seas and from Morsivs und Hninckr, Die Fische der Ostsee *). 
1) Roprer. Sur la pression osmotique du sang et des liquides internes des 
poissons sélaciens. Comptes rendus. Dec. 1900. p. 1008. 
2) G. Gruss. Ueb. d. Einfluss gelöster Stoffe auf die rothen Blutzellen. Pflüger’s 
Archiv. 63. 1896. p. 86. 
5) M. Knupsey. Hydrogr. Tab. Kopenhagen 1901, Perrersson in Scottish geogra- 
phical Magazine 1894. X.; Moregius u. Heineke. Fische d. Ostsee. Berlin 1883. 
