412 TRANSACTIONS OF THE CANADIAN INSTITUTE. [Vou. VIII. 
The distribution of the chlorides in striated muscle, therefore, as 
evidenced in the preparations obtained may occur either in the dim 
band chiefly, or alone, or in the light and dim band, the distribution 
depending, apparently, upon the phase of activity existing in the fibril 
at the moment of fixation. 
IV—THE LOCALIZATION AND THE DISTRIBUTION OF THE 
POTASSIUM 
An exceedingly sensitive reagent to shew minute traces of potas- 
sium was introduced into microchemistry by Macallum ™ in his work on 
the distribution of that element in plant and animal tissue. This 
compound, the hexanitrite of cobalt and sodium, Co Na, (No,),, with 
even a minute quantity of potassium either free or in combination gives 
an orange-yellow precipitate, which is rendered more evident by adding 
ammonium sulphide, after the tissue has been washed from every trace 
of the uncombined cobalt salt. The resulting black sulphide indicates 
the distribution of the potassium. The method of preparing the 
reagent employed was the same as that used by the above mentioned 
author, and full details are given in the account of his work. It is 
prepared by dissolving twenty grammes of cobalt nitrite and thirty-five 
grammes of sodium nitrite in seventy-five c.c. of water containing ten 
c.c. of glaciol acetic acid. The solution was then diluted to 100 c.c. 
In the early part of the work the reagent used was of this composition, 
but owing to its somewhat slow penetrability into the muscle fibrils, 
better results were subsequently obtained with a solution diluted with a 
third or one-half of a fifty per cent. solution of sodium nitrite. Care 
was taken that every trace of the uncombined cobalt reagent was 
removed from the tissue before it was treated with the ammonium 
sulphide, as otherwise a reaction would take place between the uncom- 
bined cobalt salt and the sulphide, thus giving a black precipitate. The 
preparations were mounted in fifty per cent. glycerine. 
From the various analyses of striated muscle, potassium forms one 
of the predominating elements amongst the inorganic constituents and 
because of this preponderance the tissue readily lends itself to micro- 
chemical investigation of this metal, which gives most distinct and 
characteristic results. Macallum has already shewn that these salts are 
definitely distributed in muscle. The same author has also pointed out 
that the cobalt reagent gives with creatin a constituent of vertebrate 
muscle, a precipitate similar to that obtained with the potassium salts. 
