IMMUNITY AND SUSCEPTIBILITY. 73 It need scarcely be pointed out that a loophole of doubt •exists in all these illustrations: the bacteria may have been dead before the cells ingested them, and the phenomena of digestion and destruction which have gone on in their in- teriors may have been exerted upon dead bacteria. To the relapsing-fever illustration we may take exceptions, and state that the apyrexia may have marked the death of the spirilla, which were taken up by the leucocytes only when dead. In the erysipelas illustration the streptococci remote from the centre of the lesion may have met from the body-juices or some other cause a more speedy death than that from the digestive juices of the leucocyte. Metsclmikoff, however, is prepared to show us that the leucocytes do take up living pathogenic organisms. He .succeeded in isolating two leucocytes, each containing an anthrax spore, and conveying them to artificial culture- media, where he watched them. The new environment being better adapted to the growth of the spore than for the nourishment of the leucocyte, the latter died, and the spore developed under his eyes into a healthy bacillus. Seeing that the animal cells take up bacteria, and seeing that the ameba can ingest and digest u threads of lepto- thrix ten times as long as itself," we need only put two and two together to see that MetschnikofPs theory rests upon a very substantial foundation. The more virulent the bacteria, the less ready the leucocytes are to seize them. The more immune the animal, the greater is the affinity of the leucocyte for the bacteria. The organisms which are seized upon by the leucocytes do not remain in the blood, but are collected in the spleen and the lymphatic glands; and not the least important fact in favor of phagocytosis is that observed by Bardach, that excision of the spleen diminishes the resistance to infectious disease. Quinin also furnishes a therapeutic support to the theory. It is known that quinin increases the destruc- tion of leucocytes. Woodhead inoculated a number of rabbits with anthrax, giving quinin to some of them.