Ion-PROTEID COMPOUNDS 545 
weight of water in an equimolecular KCl solution. In an 
equimolecular CaCl, solution it lost about 20 per cent. of 
water. In a LiCl solution it neither lost nor absorbed any 
water. The same was true for the bromides and iodides of 
the same metals. Even organic compounds of these metals 
showed somewhat the same difference, although the effects 
of the anion in these cases modified the results quantita- 
tively. This difference between the effects of the various 
metal ions upon the absorption of water by the muscle 
shows a remarkable parallelism with the influence of the 
same ions upon the absorption of water in soaps. There are 
Na, K, Ca and other soaps. While K soaps absorb enor- 
mous quantities of water the Na soaps absorb much less 
and the Ca soaps still less than the Na soaps. If in the Na 
soap we substitute K ions for the Na ions, the soap takes up 
quantities of water. If we substitute Ca ions for Na ions, 
the soap loses water. From this I concluded that in the 
muscle the various metal ions exist in combinations in which 
they can as easily be substituted for each other as in the 
soap compounds. These compounds are similar to the soap 
compounds in one physical quality, namely, the absorption 
of water. I expressed the opinion that the ions in muscle 
must be in combination with proteids. Ifa muscle be put 
into a KCl solution, the K ions of the solution enter the 
muscle and gradually take the place of the Na and Ca ions 
in these metal proteids. The K proteids are able to bind 
more water than the Na or Ca proteids. If the muscle be 
put into a solution of CaCl,, Ca ions will take the place of 
the Na and K ions in the proteid compounds of the muscle, 
and the muscle must lose water. I have carried these ex- 
periments farther and may publish some of the more recent 
results in this series of articles. 
T next applied this conception of ion-proteid compounds 
to a phenomenon which had hitherto been observed only 
Digitized by Microsoft® 
