Full resolution (JPEG) - On this page / på denna sida - I. General and Physico-chemical - I. Osmotic Pressure
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
12 GENERAL AND PHYSICO-CHEMICAL.
by Heidenhain as being dependent upon their power of abstracting
water from the tissues.
If we admit that the cells normally contain only small amounts of
sugar and amino-acids at any one time, then, if these substances are being
continuously burned within the cells, new quantities must constantly
be taken up and in this way gradually large quantities of the mentioned
substance would be taken up and burned. If the combustion is arrested
no new quantities are taken up. The fact that certain substances
are only taken up in small quantities at a time does not prove that they
are not burned within the cells.
According to Moore and Roaf 1
the salts exist in the blood cor-
puscles in the form of " adsorpates;" these are adsorbed by the solid
constituents of the blood corpuscles. As we will see further on (page
27) an adsorbing substance can only take up a limited amount of another
substance. If, after the saturation limit is reached, more of the adsorbed
substance is added then practically no more is taken up. In this way
we can explain why the blood corpuscles only take up very little of the
salts added. The slight ability of the sugars and amino-acids to be
taken up can perhaps be explained in a similar manner.
Osmotic Pressure of Animal Fluids. As is apparent from the
above, a substance exerts upon living cells an entirely different influence,
depending upon whether the substance is able to pass into the cell or
not, and whether the substance which does not pass in has the ability
of attracting water or not. Therefore that part of the osmotic pres-
sure of body fluids which is caused by bodies not passing in is called
the effective osmotic pressure. In this manner therefore the salts of the
alkalies and alkaline earths and the sugars act. As sugar, as well as the
bodies which according to the just mentioned experiments are readily
taken up by the cells, occurs under ordinary conditions only in very
small amounts in the blood, and also as the proteins are practically with-
out influence upon the osmotic pressure, the normal osmotic pressure of
the blood is chiefly due to the salts. As the depression of the freezing-
point is almost the only method used for animal fluids, therefore ordinarily
the freezing-point depression (A) is given as a measure of the osmotic
pressure. For mammalian blood A is constant with the exception of slight
variations flue to the food and perhaps also to other circumstances. It
is 0.56 ,
2
which corresponds to a 0.90 per cent NaCl solution and to an
osmotic pressure of about 6| atmospheres. In lower animals A may
be slightly lower, for example, in the frog A = 0.46°. In invertebrate
sea animals the body fluid is equal to the osmotic pressure of the sur-
1
Bioch. Journ., 3, 55 (1908).
J
Hamburger, Osmotischer Durck u. Ionenlehre, 1, 456.
<< prev. page << föreg. sida << >> nästa sida >> next page >>
