224 Prof. A. B. Macallum. On the Nature of the [Mar. 3, 
possible to extract them with water free from haloids, and thereby greatly 
affect the silver reaction of the tissues so treated. In the case of vegetable 
stems also, the salts may be extracted with alcohol of 98-per-cent. strength, 
which, of course, leaves in the preparations their proteids and carbohydrates. 
and sections made from vegetable tissues (¢.g., Tulipa), and at once treated 
with alcohol for 24 hours, usually give no reaction with the silver reagent. 
This is true also of animal tissues, thin sections of which, made from fresh 
material frozen with carbon dioxide spray, after lying in alcohol of 90 per 
cent. for some days, are practically unaffected in a silver solution placed 
in the sunlight. Stronger alcohol, even of 98-per-cent. concentration, also 
removes the chlorides if the pieces of tissue be small or in thin sections, 
but if the pieces be of considerable thickness, the alcohol removes only a 
small portion of the salts and redistributes the remainder throughout the 
preparations. | 
The question is, however, not whether the haloids in tissues constitute: 
a factor in the silver reaction, but rather whether apart from the exceptions. 
referred to they are the only compounds which contribute to the reaction. 
The proteids, as already pointed out, are regarded as possessing the 
property of forming reducible compounds with silver, and to determine 
whether this view is correct, the purification of a number of typical proteids. 
and of an albuminoid was undertaken. 
For this purpose it was necessary, first of all, to have every fluid and 
reagent that was used free from chlorides to the extent that these were 
below the minimum limit of detection, that is, if chlorine should be present. 
as chloride it would be less than 1 in 1,600,000. This is possible in the case 
of carefully distilled water, but it is not quite as easy in the case of the 
precipitating reagents employed, namely, anhydrous sodium sulphate* and 
ammonium sulphate. In the case of the former, the “chemically pure ” 
material had to be repeatedly crystallised before it was obtained in a form 
sufficiently free from chlorides. Many of the “chemically pure” prepara- 
tions of ammonium sulphate put on the market are not of the standard of 
purity required, and different quantities of the salt from the same. 
manuiacturer were found to vary considerably as regards. relative purity. 
In every case, however, only those preparations of the salt were used which 
reached the standard exacted. 
The material employed consisted of egg “albumen,” serum “albumen,” 
and gelatin. In the case of egg “albumen” the solution was first of all made 
* On the employment of anhydrous sodium sulphate as a precipitant of proteids from 
their solutions, see Pinkus: ‘On the Precipitation of Proteids,” ‘Jour. of Physiol.,” 
vol. 27, p. 57, 1901 to 1902. 
