XIV. THE BLOOD VESSELS 
■» i 
< 
A. GROSS ANATOMY OF THE ARTERIES AND VEINS. 
Preparation of Material (Cat, Rabbit, White Rat, or Guinea 
Pig) .—The study of the circulatory system of an animal is greatly 
facilitated by filling and slightly distending the blood vessels, 
previous to dissection, with some fluid which will solidify within 
the vessels and which, being brightly colored, will enable the 
student to follow the course of the various vessels with ease. 
Such a fluid injection mass may, moreover, be distinctively colored 
to differentiate the various parts of the circulatory system. 
There are many different injection masses used, the chief 
requisite in preparation for gross dissection being (i) that the 
liquid should flow freely through the small tubes or cannulas used 
to introduce it into the various vessels; (2) that the fluid should 
contain suspended particles too large to pass through the capillary 
vessels into the tissues; (3) that the coloring matter should not be 
soluble, as it would then not remain confined to the blood vessels, 
but would stain the surrounding tissues; (4) that the mass should 
solidify within the vessels, but not too rapidly. 
The following injection mass 1 fills the above requirements 
satisfactorily. Make a gelatine solution of one part gelatine to 
seven or eight parts (by weight) of water. Soak the sheets of 
gelatine in the cold water and gradually heat it until the gelatine is 
dissolved, taking care not to burn it. To one volume of dry corn 
starch (mixed with an amount of powdered dry pigment sufficient 
to give the requisite depth of color) add three or four volumes of 
the warm (but not boiling) gelatin solution. Mix thoroughly 
and strain, while the mixture is still warm, through a fine wire 
strainer into a small clean jar, which, to be used conveniently, 
should be wide mouthed and should not be filled more than half 
full. The mixture thus made may be kept for several days by the 
1 Cf. Rand, The Skate for Classes in Comparative Anatomy; injection methods. 
American Naturalist, Vol. XXXIX, p. 365, 1905. 
102 
