There is no question that the corpuscles engage in conflict with the bacteria when they thus surround them.  There has been not a little dispute, however, as to the method by which they carry on the conflict.  It has been held by some that the corpuscles actually take the bacteria into their bodies, swallow them, as it were, and subsequently digest them (Fig. 33 c, d, e).  This idea gave rise to the theory of phagocytosis, and the corpuscles were consequently named phagocytes.  The study of several years has, however, made it probable that this is not the ordinary method by which the corpuscles destroy the bacteria.  According to our present knowledge the method is a chemical one.  These cells, when they thus collect in quantities around the invaders, appear to secrete from their own bodies certain injurious products which act upon the bacteria much as do the alexines already mentioned.  These new bodies have a decidedly injurious effect upon the multiplying bacteria; they rapidly check their growth, and, acting in union with the alexines, may perhaps entirely destroy them.

After the bacteria are thus killed, the white blood-corpuscles may load themselves with their dead bodies and carry them away (Fig. 33 d, e).  Sometimes they pass back into the blood stream and carry the bacteria to various parts of the body for elimination.  Not infrequently the white corpuscles die in the contest, and then may accumulate in the form of pus and make their way through the skin to be discharged directly.  The battle between these phagocytes and the bacteria goes on vigorously.  If in the end the phagocytes prove too strong for the invaders, the bacteria are gradually all destroyed, and the attack is repelled.  Under these circumstances the individual commonly knows nothing—­of the matter.  This conflict has taken place entirely without any consciousness on his part, and he may not even know that he has been exposed to the attack of the bacteria.  In other cases the bacteria prove too strong for the phagocytes.  They multiply too rapidly, and sometimes they produce secretions which actually drive the phagocytes away.  Commonly, as already noticed, the corpuscles are attracted to the point of invasion, but in some cases, when a particularly deadly and vigorous species of bacteria invades the body, the secretions produced by them are so powerful as actually to drive the corpuscles away.  Under these circumstances the invading hosts have a chance to multiply unimpeded, to distribute themselves over the body, and the disease rapidly follows as the result of their poisoning action on the body tissues.