Further evidence for the origin of the lymphocytes of the blood from the lymphatic glands is to be obtained from those cases in which we find an increase of the lymphocytes in the blood. These "lymphocytoses" occur, in comparison with other leucocytoses, relatively seldom. Under certain conditions in which a hyperplasia of the lymphatic glandular apparatus makes its appearance, we often see at first an increase of the lymphocytes in the blood. Ehrlich and Karewski in some unpublished work have investigated together a large number of typical cases of lymphoma malignum, and were able constantly to observe a lymphocytosis, which in some cases was of high degree and bore almost a leukæmic character.
Relying on these facts Ehrlich and Wassermann (_Dermatolog. Zeitschr._ Vol. I., 1894) made the diagnosis _in vivo_ of malignant lymphoma in a rare skin disease, chiefly from the absolute increase of the lymphocytes alone, although no swelling of the glands was palpable. The post-mortem shewed that the chief condition was a swelling of the retro-peritoneal lymph glands to lumps as large as a fist.
The lymphocytosis following extirpation of the spleen also belongs to this category, since a vicarious enlargement of the lymph glands is always to be observed in these cases.
On investigating the conditions under which in healthy individuals an increased number of lymphocytes enter the blood-stream, we have in the first place to notice the digestive canal, whose wall contains a thick layer of lymphatic tissue. According to the results of Rieder the proportion of the lymphocytes to polynuclears is practically normal in the leucocytosis of digestion, indeed the lymphocytes are rather in excess. The eosinophils on the other hand shew a marked relative reduction in this condition. The leucocytosis of digestion consequently differs essentially from the other kinds, in which the neutrophil elements are chiefly increased. The simultaneous increase of lymphocytes and polynuclears is doubtless brought about by a super-position of a raised income of lymphocytes, and an ordinary leucocytosis caused by the assimilated products of metabolism.
The influence of the digestive tract is still more evident in certain diseases, more particularly in intestinal diseases of infants. A considerable increase of the lymphocytes in the blood-stream is here to be observed. Thus Weiss found an important increase of the white blood corpuscles in simple catarrh of the stomach and intestines, which presented the main features of a lymphocytosis.