INJECTING. 121 
the first two bottles is filled and acts as a siphon and thus 
conveys the water to the second bottle creating there a pres- 
sure which in turn is communicated to the bottle, e, which 
contains the injecting material and which is thus forced out 
into the subject. By elevating or depressing the bottle 4 any 
desired pressure may be obtained. 
With the injecting apparatus a colored fluid is forced into 
the vessels, rendering it very easy to trace them in dissecting. 
In some cases a saturated solution of prussian blue is suffi- 
cient for this purpose but it is better to employ albumen or 
gelatine as a basis. 
Common gelatine is melted over a slow fire with the aid 
of water, in the proportions necessary to make a stiff jelly 
when cold. ‘These proportions are usually given on the out- 
side of the package. When melted, the coloring matter is 
stirred in. This may be an aqueous solution of carmine or 
prussian blue. Vermilion and yellow ochre are sometimes 
used but from their weight they are not readily held in 
suspension. 
In injecting with gelatine the object must be first warmed 
and then kept in warm water while the operation is being 
performed, otherwise the jelly will set before the fine vessels 
are filled. ‘To ensure success the specimen injected should 
be fresh, not alcoholic. When injected, the vessels should be 
tied and the specimen put away to cool so that the jelly may 
set. It is well to place it immediately in alcohol as that 
reagent facilitates the process by the extraction of water. 
The place for the introduction of the injecting fluid varies 
with the form operated upon, as well as the system to be 
