LYMPHATIC AND LACTEAL SYSTEM. 
Fig. 50. 
Exhibits three forms of valves of very frequent occur- 
rence in the lymphatics, especially in the neighbour- 
hood of glands, and which are not described in 
works on Anatomy. ( Taken from specimens pre- 
pared for the microscope.) Magnified ten diameters. 
A. a, the interior of the vessel. 06, b, the 
valvular flaps composed of the lining membrane 
only. The attached, the unattached edges, as well 
as the surface of these flaps, are on the same plane ; 
they do not perfectly close the vessel. 
B. a, the interior of the vessel. 6, the valvu- 
lar flap of a circular form, resembling the dried 
pyloric valve of the stomach; apparently com- 
posed of the fibrous as well as the inner tunic. 
C represents 4 combination of the two former. 
a, the interior of the vessel. 6. valvular flaps re- 
sembling those of A. c, a third fold resembling 
the circular fold of B. 
in diameter they are frequently not more than a 
line apart, while in others of half that magni- 
tude there may be an interval of an inch between 
them. It has been observed that they are more 
frequent and closer together in the larger lym- 
phatics than in the smaller; this is not always 
the case; for instance, the lymphatics of the 
_ upper extremity, which are much smaller than 
those of the lower, have less intervals between 
their valves ; and in the neck, where the vessels 
are still smaller, the valves are less distant apart. 
It appears to me that the valves are much more 
approximated to each other in the neighbour- 
hood of the glands, and this observation-applies 
to the vasa afferentia as well as to the vasa effe- 
rentia, but especially to the latter; from which 
circumstance the notion may have arisen, that 
the valves are more frequent the larger the 
vessel. The valves recur less frequently in the 
thoracic duct than in any other part of the 
system. It is not uncommon to find in this 
vessel an interval of two or three inches in 
extent without a valvular fold. 
Mode of origin of the lymphatics—The- 
‘plan I have hitherto adopted in describing 
‘the lymphatic vessels has been to present to 
the reader, first, that which is most readily 
211 
understood, because easily recognizable by our 
senses, and about which there could be little 
difference of opinion; but I have now to direct 
attention to a part of our subject which has 
hitherto baffled the efforts of all inquirers, viz. 
the mode of origin of the anise vessels, 
concerning which the sight, aided by the most 
powerful glasses, has failed to supply us with 
satisfactory and demonstrable information. The 
numerous opinions and conjectures on this sub- 
ject, only present us with so many instances, of 
the vain struggles of the human mind, to ad- 
vance in a strict science of observation, beyond 
the limits assigned to our senses, and of the 
unwillingness, even in the philosopher and man 
of science, to acknowledge the weakness and 
limited range of his faculties. 
When we consider the transparency of the 
coats of the lymphatic vessels, as well as of their 
contents, the small size of their secondary 
branches, and the numerous valves they every 
where present, we cannot feel surprised that 
their precise origin should be involved in 
much obscurity. From the opaque nature of 
the chyle, it might be imagined that while the 
vessels were distended with this fluid, the 
anatomist would be enabled to trace them to 
their commencing branches, but unfortunately, 
it is almost impossible to prevent the onward 
motion of the chyle in the vessels first re- 
ceiving it, while the valves offer a complete 
harrier to any retrograde movement. Added to 
which, the opacity of the coats of the intestine 
renders it extremely difficult to follow these 
vessels from the peritoneal surface of the outer, 
to the villous surface of the inner tunic, even 
when distended with chyle. Transparency of 
the coats of the intestine may be obtained by 
drying, but the chyle becomes transparent at 
the same time. Various modes of investigation 
have been adopted by anatomists to overcome 
these difficulties, the principal of which it may 
be necessary here to mention. Injections of 
quicksilver ot coloured fluids have been thrown 
into the arteries, by which means the injection 
has occasionally made its appearance in the 
lymphatic vessels: this result occurs, accord- 
ing to Panizza, in a particular organ in an 
animal of one species, while in another the 
experiment will succeed, not in the same, but 
in some other organ. Thus he succeeded in 
filling the lymphatics from the arteries, in the 
intestines of the dog and pig; in the liver of 
man, the horse, and dog ; in the testicle of the 
dog and bull; in the penis and spleen of the 
horse. He was unsuccessful in the intestines 
of man, the horse, birds, the salamander, and 
the tortoise; in the liver of reptiles; in the 
spleen of man, the dog, and the pig; in the 
kidneys of mammalia and birds; in the penis 
of man and the dog. 
Breschet is of opinion that injections by the 
veins pass more readily into the lymphatic sys- 
tem. Ihave now in my possession two prepa- 
rations where the lymphatics have been acci- 
dentally injected from the veins; one in the 
mesentery of the turtle, the other in the kidney 
of. man; and I have undoubtedly observed 
this occurrence much more frequently after in- 
P 
