96 
COMPARATIVE ZOOLOGY. 
The lacteals are only a special part of the great lym¬ 
phatic system, which absorbs and carries to the thoracic 
duct matter from all parts 
of the body . 52 The lymph 
is a transparent fluid having 
many white blood corpus¬ 
cles. It is, in fact, blood, 
minus the red corpuscles, 
while chyle is the same fluid 
rendered milky by numer¬ 
ous fat - globules. During 
the intervals of digestion, 
the lacteals carry ordinary 
lymph. This fluid is the 
overflow of the blood —the 
plasma and white corpus¬ 
cles which escape from the 
blood capillaries, and carry 
nutriment to, and waste from, 
those parts of the various 
tissues which are not in con¬ 
tact with the blood capilla¬ 
ries. This surplus overflow 
is returned to the blood by 
Fig. 61. Principal Lymphatics of the Iln- the lymphatics. The Current 
man Body: a, union of left jugular and t *' 1 
subclavian veins; b, thoracic duct; e, is kept lip by the movements 
receptaculum cliyli. The oval bodies .. . . . 
are glands. ox the body, and in many 
Vertebrates, as Frogs and Fishes, by lymph hearts . 
Like the roots of Plants, the absorbent vessels do not 
commence with open mouths; but the fluid which enters 
them must traverse the membrane which covers their mi¬ 
nute extremities. This membrane is, however, porous, 
and the fluids pass through it by the forces of filtration 
and diffusion . 53 How the fat gets into the lacteals is not 
yet well understood, but the lacteals are themselves rhyth¬ 
mically contractile, and force the absorbed chyle towards 
