st always traumatic,
and is treated by excision of the sac.

CHAPTER XV

THE LYMPH VESSELS AND GLANDS

Anatomy and Physiology--INJURIES OF LYMPH VESSELS--_Wounds of
thoracic duct_--DISEASES OF LYMPH VESSELS--Lymphangitis:
_Varieties_--Lymphangiectasis--Filarial
disease--Lymphangioma--DISEASES OF LYMPH
GLANDS--Lymphadenitis: _Septic_; _Tuberculous_;
_Syphilitic_--Lymphadenoma--Leucocythaemia--TUMOURS.

#Surgical Anatomy and Physiology.#--Lymph is essentially blood plasma,
which has passed through the walls of capillaries. After bathing
and nourishing the tissues, it is collected by lymph vessels, which
return it to the blood stream by way of the thoracic duct. These lymph
vessels take origin in the lymph spaces of the tissues and in the
walls of serous cavities, and they usually run alongside blood
vessels--_perivascular lymph vessels_. They have a structure similar to
that of veins, but are more abundantly provided with valves. Along the
course of the lymph trunks are the _lymph glands_, which possess a
definite capsule and are composed of a reticulated connective tissue,
the spaces of which are packed with leucocytes. The glands act as
filters, arresting not only inert substances, such as blood pigment
circulating in the lymph, but also living elements, such as cancer cells
or bacteria. As it passes through a gland the lymph is brought into
intimate contact with the leucocytes, and in bacterial infections there
is always a struggle between the organisms and the leucocytes, so that
the glands may be looked upon as an important line of defence, retarding
or preventing the passage of bacteria and their products into the
general circulation. The infective agent, moreover, in order to reach
the blood stream, must usually overcome the resistance of several
glands.

Lymph glands are, for the most part, arranged in groups or chains, such
as those in the axilla, neck, and groin. In any given situation they
vary in number and size in different individuals, and fresh glands may
be formed on comparatively slight stimulus, and disappear when the
stimulus is withdrawn. The best-known example of this is the increase in
the number of glands in the axilla which takes place during lactation;
when this function ceases, many of the glands become involuted and are
transformed into fat, and in the event of a subsequent lactation they
are again developed. After glands have been removed by operation, new
on