( 378 ) 
repeated bleeding contain considerably less urea, than is normally 
the case. 
From the dorsal artery of the animals, with which 1 experimented, 
the blood was collected, from which after defibrination with glass 
beads the blood serum was obtained by centrifugation. Only then 
the resistance and the freezing point were determined by the usual 
methods. Part of the serum was then tested for its percentage of 
urea. This was done by determining by Kjehldahl’s method the 
N-percentage after the albumen had been removed. From an oral 
communication of Dr. Burian I knew that in albumen-free blood 
serum and in the urine of Scyllium no other N-compounds than 
urea are present in measurable quantities. 
The albumen was precipitated a few times by Hofmeister’s method, 
in which sodium acetate and ferric chloride are added to the liquid 
and then a precipitate is formed by heating with a little sodium 
carbonate. The filtrate was absolutely clear and free from albumen. 
The value obtained in this way for the percentage of urea was 
smaller, however, than when the albumen was precipitated cold by 
alco.iol and acid or according to Baglioni by a hydrochloric solution 
of asaprol. 
Many times the ash percentage of the serum was tested by turning 
all the salts into sulphates by means of nitric and sulphuric acid 
and weighing. It is clear that a comparison of the lowering of the 
freezing point and the ash percentage indirectly gives an idea of the 
urea concentration of the serum. 
In the same way the ash percentage and resistance give an idea 
of the quantity of albumen, since with equal quantities of dissolved 
salt the electric resistance of the liquid can only change by varying 
the quantity of non-electrolytes (colloids). 
In the following summary of the experiments A means the freezing 
point, always determined in the same way with a bath temperature 
of 5° to — 6^, an undercooling of — 0.5°, while the stirring rod 
moved up and down about twice per second. The freezing was 
induced by inoculating with a splinter of ice. 
R is the resistance expressed in 42, determined according to Kohl- 
rausch’s method and calculated by means of Obachts’ tables. V 
the percentage of urea (behind the figure is indicated by H or i 
whether the albumen was precipitated by Hofmeister’s method or 
by asaprol), S is the salt concentration expressed as sulphates, A the 
g-lbumen, 
