The strife became a national one between the French and Germans,--on the one side in France the phagocytic theory was defended, and in Germany, on the other, the theory of serum immunity.

The mass of experimental work which poured from the laboratories of the two countries in attack and defence became so great that it could not easily be followed.

It had a good influence because, without the stimulation of this national rivalry, the knowledge which gradually arose from this work would not have been so quickly acquired.

It is interesting that the mode of action of the serum in destroying bacteria was demonstrated not by a German but by Bordet, a French observer and a pupil of Metschnikoff.

He showed that the serum contained two distinct substances, each necessary for the destructive action.