536 | Proteins 
gelatin is afterward perfused several times with distilled water. 
It would, therefore, follow that gelatin treated by neutral salts 
with bivalent cations increases its mass of gelatin ions either not 
at all or only to a negligible extent. This is apparently the case. 
When 2 gm. of powdered gelatin are first perfused twice with m/8 
CaCl, and are then perfused three times with 25 cc. of distilled 
water, and if then a 3 per cent gelatin solution is prepared, 5 cc. of 
such a solution are precipitated by slightly less than 5 ce. of alco- 
hol (at room temperature), which is approximately the same figure 
as that for gelatin not treated with salt. The gelatin is, therefore, 
apparently not ionized by Ca. 
5. This difference in the action of neutral salts with bivalent 
and univalent cations, namely, that the latter ionize the gelatin 
while the bivalent cations will apparently not form ionizable com- 
pounds, is the basis of the antagonistic action between the two types 
of salt. When we treat powdered gelatin with a mixture of NaCl 
and CaCl, the addition of a comparatively small amount of CaCl, 
to M/8 NaCl will inhibit the swelling which would follow if the 
gelatin were perfused first by the NaCl alone and then by dis- 
tilled water. It can be shown that when we perfuse 2 gm. of 
powdered gelatin twice with 25 cc. of 50 cc. M/8 NaCl + 4 ee. 
M/8 CaCle, and then three times with distilled water, the gelatin 
is precipitable by alcohol; while if we use the pure M/8 NaCl or 
50 cc. M/8 NaCl.+ 1 or 2 ce. of m/8 CaCl, the 3 per cent gelatin 
solution freed from the salt is not precipitable by alcohol. We, 
therefore, come to the conclusion that the phenomenon of swell- 
ing of gelatin under the influence of neutral salts with univalent 
cation and the inhibition of this swelling by neutral salts with 
bivalent cation (alkaline earths) are due to the fact that the former 
salts cause the formation of ionizable gelatin salts, while the 
latter apparently cause the formation of non-ionizable gelatin salts. 
Tl: 
We may raise the question: Which of the possible cases of 
ionization actually occurs when gelatin is treated with neutral 
salts with univalent cation, like NaCl? If we assume that the 
gelatin molecule combines with both anion and cation the neutral 
Na 
complex golating can give rise to three types of protein ions: 
