But chemiotaxis may be exerted from within the bloodvessel as well as from without. Bouchard, Massart and Bordet have shown that a tube containing a culture of bacillus pyocyanus, introduced beneath the skin of a rabbit attracts in a few hours a great number of leucocytes. But if, immediately after its introduction, ten cubic centimetres of a sterilized culture of the same bacillus are injected into a vein, very few leucocytes enter the tube inserted under the skin. The chemiotaxis seems to operate in this case from within the blood, and the desires of the leucocytes are satisfied without leaving the vessel. It would seem that in such cases the migration and protective work of the leucocytes is best exerted at the outset of the illness and before the toxic products have been poured into the blood in any quantity, whereas in the advanced stages when the blood is charged with ptomaines and toxins migration and phagocytosis would be likely to be limited and ineffective. The same consideration would forbid the use of drugs that check migration in all cases of attacks by microbes for which leucocytes have a positive chemiotaxis. =Phagocytosis= is the act by which the leucocytes englobe and dissolve the invading microbe. By its amœboid movement the leucocyte flows around, and envelopes the microbe for which it has a positive chemiotaxis, and then begins the struggle of vitality between the two living germs. If the poison (leucomaine antitoxin,) and digestive ferment (enzyme) of the leucocytes are more deadly to the invading germ, than its ptomaines, toxins and enzymes are to the leucocyte, the white cell comes off the victor, and recovery takes place, but if the converse obtains the triumph is on the side of the microbe. As a rule much depends on the more or less deadly nature of the products of the invading microbe, on the numbers of the germ, the rapidity of its proliferation, and the consequent amount of its toxic products thrown into the system, on the one hand: And on the other the potency of the chemiotaxis of the leucocyte for the invading germ, the number of white cells that emigrate into the inflamed tissue and engage in the work of phagocytosis, and on whether the particular animal system and its white cells have sustained a previous attack by the same germ and has thereby been educated to produce a greater amount of the defensive proteids (leucomaine, antitoxin, enzyme) than it naturally would (acquired immunity). Even with an abundant emigration of the leucocytes into the inflamed or invaded tissue, a number, greater or less, are usually destroyed by the bacterial poisons and pass into degeneration or liquefaction, as in the formation of pus, and yet the attacking germ may be overcome, destroyed and devoured by the rapidly increasing survivors. In general terms the migration of the cells is in inverse ratio to the susceptibility of the animal to the microbe or the disease which it causes.