(2.) The second variety, consisting of leucæmic lymphadenitis, or leucocythæmia, is a lymphatic lucæmia or lympho-cythæmia, the anatomical characteristic of which is enlargement of lymphatic glands, and the histological characteristic increase in number of the large and small lymphocytes.
(3.) A third variety, formerly regarded as simple leucæmia without lymphadenitis, is myelogenic leucæmia or myelo-cythæmia, the anatomico-pathological characteristic of which is to be found in myeloid hypertrophy of the bone marrow, giving to the bone marrow on post-mortem examination a puriform appearance, and in the myeloid condition of the spleen.
Histologically this variety is characterised by an absolute increase in numbers of the large mono- and poly-nuclear eosinophile leucocytes.
Symptoms. Simple lymphadenitis begins in an insidious manner, and is characterised by weakness, anæmia, paleness of the mucous membranes, and wasting without apparent reason, although the appetite is preserved. It is only at a later stage that the glandular enlargements are discovered (adenitis), and often this discovery is not made until the veterinary surgeon is called in.
The existence of the disease is indicated by enlargement of the superficial glands, and this enlargement, which may commence at any point, extends along the course of the lymphatic vessels to the neighbouring glands, until in a shorter or longer time it involves all the lymphatic glands in the body.
The enlargement of the glands is usually symmetrical, and on clinical examination it is sometimes easy to detect at the outset an increase in size of the retro-pharyngeal glands, the glands of the neck, the prescapular glands, the glands of the flank, etc.
Rectal exploration reveals hypertrophy of the glands of the pelvis and of the sublumbar region, etc. The animals waste very rapidly, and sometimes in a few months become incapable of standing. They develop cachexia, and die in a state of exhaustion, with no other lesions than those of lymphatic hypertrophy. Neither do they exhibit any marked increase in the number of white corpuscles in the blood.
In lympho-cythæmia the beginning of the disease is often identical with that of simple lymphadenitis, the increase in the number of white blood corpuscles not occurring until later. In other cases, on the contrary, leucæmia appears first, and the enlargement of the lymphatic gland follows; but what characterises this form and allows of it being distinguished from myelo-cythæmia is the great increase in the number of large or small lymphocytes. The development is identical with, and sometimes much more rapid than, that of the preceding form. The animals waste away and become anæmic and cachectic, dying at last in a state of absolute exhaustion.
Post-mortem examination reveals, as in the previous condition, symmetrical hypertrophy of all the lymphatic glands; the spleen is very often enormous, and the liver is sometimes affected, as are also, in exceptional cases, the kidneys.
It may happen that the spleen alone appears affected, or at least that it has been first attacked, a fact which explains the existence of leucæmia before any enlargement of the lymphatic glands.