1877.] The Study of Zodlogy in Germany. 403 
motion takes place, some of the liquid in the cavities of the con- 
nective tissue is pressed into the lymphatics and so slowly driven 
onwards into the heart. To counterbalance this loss of intercel- 
lular fluid, certain constituents of the blood exude through the 
walls of the capillaries and keep up the supply. There is, 
therefore, a double circulation: one within the blood-vessels, and 
another from the walls of the capillaries through the lymphatics. 
The liquid in both circulations is ultimately returned to the 
heart. 
Different methods have to be employed for injecting the two 
systems. In the case of the blood-vessels a rather large syringe 
may be used, provided with a point small enough to pass into the 
artery of the part to be injected. The artery should be carefully 
laid bare and cut about half way through; the point of the 
syringe, which, must be previously filled with the injection mass, 
is pushed into the artery and firmly tied in place. In many 
cases it is quite sufficient to inject a cold saturated solution of 
Prussian blue in water, or when more perfect preparations are 
wanted, a little gelatine may be added; in this case, however, 
there arises the inconvenience that both the injection mass and 
the organ to be injected have to be kept warm while the opera- 
tion is going on, otherwise the gelatine solidifies. 
To prepare a “ warm ” injection mass, the following method is, 
perhaps, the best. A solution of Prussian blue is necessary ; 
this the histologist must make for himself. To do this take a 
concentrated solution of sulphate of protoxide of iron in dis- 
tilled water, and pour it slowly into a concentrated solution of 
yellow prussiate. of potassium; a precipitate of insoluble Prus- 
sian blue is formed. There should be a small excess of prussiate 
at the end of the operation, to test which take out a drop and 
add to it a little of the sulphate. If there is any free prussiate 
-still present, a blue precipitate is thrown down. Filter through a 
felt strainer, below which a funnel with a paper filter has been 
Placed. Pour water on to the strainer in small quantities at a 
time, and continue filtering ; this operation must be kept up for 
Several days, until the liquid below the second filter appears dis- 
tinctly blue. The matter on the felt strainer is then removed 
_ and dissolved in distilled water. This solution is admirable for 
cold injections or for filling the lymph-vessels, as will be de- 
scribed presently. There should always remain an excess of 
blue in the vessel in order to be sure that the solution is satu- 
fated; as the solution is removed it may be replaced by dis- 
