( 381 ) 
says, that this polyuria is probably caused by “eine Schadigung der 
Wasserresorption, indes die 'Resorption geloster BestandteiLe vor sich 
geht.” With the fishes mentioned, and with amphibia this explanation 
might also assist us to understand the relation of the constituents of 
the urine and of the blood serum. It was important to know to 
what extent this retro-resorption did not take place with a quicker 
flow of urine, thus causing the constitution of the urine to become 
more and more equal to that of the albumen-free blood serum. 
The urind of big specimens of ScyIlium canicula was collected by 
a method which is usually applied in the Zoological Station at Naples. 
By a special shape of the canule it was possible to collect the urine 
of female animals. This made it certain that no sperm or mucus 
came into the urine, which accordingly was always clear and free 
from albumen in the experiments. 
After a small part of the urine had been tested for albumen, the 
freezing point and the resistance were determined and then the 
percentage of nitrogen was determined by Kjehldahj/s method. 
From the values found the urea concentration was calculated. Since 
diuretics have no effect on sharks I tried to increase the secretion 
of urine by the “piqure”. After urine had been collected for one or 
two days, I took the experimental animals from the aquarium for 
a moment and pricked them with a two-edged lancet in the medulla 
tn the region of the posterior edges of the eye-sockets in the median 
line. Examination of dead animals proved that the vulneration had 
affected the lower part of the fourth ventricle or somewhat more 
towards the tail the medulla. In the most successful experiments the 
wound was on both sides and the greater part of the dorsal half of 
the medulla had been cut. 
Put back into the aquarium immediately after being wounded the 
■-lark swam about in a somewhat restless and uncoordinated manner, 
1( ^ es a sBght acceleration of respiration generally existed. These 
P enomena disappeared after 10 —30 minutes; the animal could then 
ln no way be distinguished from the healthy ones. 
n the following table, containing a summary of the results of the 
ex peiiments, A means the freezing point, R the resistance, U the 
percentage of urea, while “prick” means that the animal was wounded 
ln the above mentioned manner. 
These experiments show: 
a • The urine of Scy Ilium canicula has normally a smaller osmotic 
^ressure than the blood serum. This is caused by the considerable 
erence between the percentage of urea of the serum and of 
the urine. 
