As result of finding numerous plasma cells in the omenta of rabbits injected with tuberculo-protein, a method to induce the production of large numbers of these cells has been discovered. The tissues in which they were pronouncedly increased were the subserosal connective tissues of the omentum, body wall, and intestinal wall.

The precursor of the plasma cells is a primitive connective tissue cell. As this cell develops into the typical Marshalkó plasma cell there is a progressive increase in the basophilia of the cytoplasm, the nucleus becomes eccentric, a condensation of the chromatin occurs near the nuclear membrane, and there is a loss of the nucleoli. At the time when the nucleus assumes the eccentric position, the clear area appears in the center of the cytoplasm. The early cells are capable of reproducing themselves by mitosis, while the typical mature cells divide by amitosis.

The mature plasma cells often have muddy, spongy cytoplasm which contains acidophilic or hyaline granules as the cells grow old or begin to degenerate. The cells with granules or hyaline bodies usually have pycnotic or fragmented nuclei. These cells are the final stage reached by some plasma cells. Others, when degenerating, show vacuoles and signs of senility. Those with the granules and hyaline bodies are the so called Russell body cells.

Plasma cells developed in greatest numbers after our largest injections of tuberculo-protein. The differentiation into young, mature, and senile forms was most clearly recognizable when some days had been allowed to elapse after the last large injection of the stimulating agent.

A description of the plasma cell as viewed supravitally has been given. The cells are met in the blood stream as well as in the tissues. They are characterized by their deep yellowish gray cytoplasm, indistinct eccentrically placed nuclei, and large numbers of mitochondria.

The plasma cells differ from lymphocytes, in that they did not develop in large numbers after direct stimulation of the lymph nodes with tuberculo-protein. The young plasma cells also differ in morphology from the young lymphocytes. When plasma cells were found in the lymph nodes they were in the connective tissue cords.

The plasma cell is a definite entity, having a maturation cycle. It is stimulated to great proliferation by certain toxic irritants.

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