THE BLOOD VESSELS 
IO 3 
addition as soon as it has solidified, of a sufficient quantity of some 
coal-tar disinfectant to cover the top with a thin layer. 
When the mass is to be used, first wash the disinfectant from 
the surface by means of cold water, then let the jar stand in a pan 
of hot water (but never boiling, since that would cook the starch) 
for a few minutes to melt the gelatine. Keep the water in the 
pan hot by changing it from time to time as the work proceeds. 
Lay in the same hot water the implements to be used, such as glass 
syringes, several glass cannulas made from glass tubing drawn out 
into a tapering nozzle for insertion into blood vessels, short 
lengths of rubber tubes for connecting cannulas with syringes, 
and a sponge, or mass of absorbent cotton. Artery clamps for 
the temporary closing of a cut vessel to prevent loss of the injec¬ 
tion mass when the syringe is withdrawn, are very convenient, 
though little plugs of cotton or the simple pressure of the finger 
may be used frequently for the same purpose. 
In injecting, fill the syringe with the thoroughly stirred injec¬ 
tion mass and then attach the rubber tube, into the end of which 
the glass cannula has been inserted. 
In case the injection is to be made through a small blood vessel 
it will be necessary to insert the cannula into a slit in the wall of 
the vessel before attaching it to the syringe, since, owing to 
the collapsible nature of small blood vessels, particularly veins, the 
most effective method of inserting the cannula is by blowing the 
edges of the slit open using the cannula itself with the rubber 
attached as a blowpipe, and thrusting the point of the cannula 
in as the slit opens up. 
In case the injection is made directly into the heart or some 
large vessel, the attachment to the syringe may be made, and the 
cannula itself filled with the injection mass, before it is inserted. 
In any case, after the insertion of the cannula is made and the 
syringe is attached, the injection mass should be driven in with a 
slow steady pressure of the piston, while the cannula is firmly held 
in place with the thumb and finger. Never force the injection 
against a decided resistance but if you have reason to believe 
that the injection is not complete, halt the process and seek for 
the source of the resistance. At times, the squeezing of hot water 
from a sponge over the region which is being injected, facilitates 
