26 REPORT—1896. 
inflammatory conditions they passed through the pores in the walls of the 
finest blood-vessels, and thus escaped into the interstices of the surrounding 
tissues. Cohnheim attributed their transit to the pressure of the blood. 
But why it was that, though larger than the red corpuscles, and contain- 
ing a nucleus which the red ones have not, they alone passed through 
the pores of the vessels, or why it was that this emigration of the white 
corpuscles occurred abundantly in some inflammations and was absent 
in others, was quite unexplained. 
These white corpuscles, however, have been invested with extraordi- 
nary new interest by the researches of the Russian naturalist and patholo- 
gist, Metchnikoff. He observed that, after passing through the walls of 
the vessels, they not only crawl about like amebz, but, like them, receive 
nutritious materials into their soft bodies and digest them. It is thus that 
the effete materials of a tadpole’s tail are got rid of ; so that they play a 
most important part in the function of absorption. 
But still more interesting observations followed. He found that a 
microscopic crustacean, a kind of water-flea, was liable to he infested 
by a fungus which had exceedingly sharp-pointed spores. These were 
apt to penetrate the coats of the creature’s intestine, and project into 
its body-cavity. No sooner did this occur with any spore than it became 
surrounded by a group of the cells which are contained in the cavity of 
the body and correspond to the white corpuscles of our blood. These 
proceeded to attempt to devour the spore; and if they succeeded, in 
every such case, the animal was saved from the invasion of the parasite. 
But if the spores were more than could be disposed of by the devouring 
cells (phagocytes, as Metchnikoff termed them), the water-flea succumbed. 
Starting from this fundamental observation, he ascertained that the 
microbes of infective diseases are subject to this same process of devouring 
and digestion, carried on both by the white corpuscles and by cells that line 
the blood-vessels. And by a long series of most beautiful researches he has, 
as it appears to me, firmly established the great truth that phagocytosis 
is the main defensive means possessed by the living body against the inva- 
sions of its microscopic foes. The power of the system to produce anti- 
toxic substances to counteract the poisons of microbes is undoubtedly in 
its own place of great importance. But in the large class of cases in 
which animals are naturally refractory to particular infective diseases the 
blood is not found to yield any antitoxic element by which the natural 
immunity can be accounted for. Here phagocytosis seems to be the sole 
defensive agency. And even in cases in which the serum does possess 
antitoxic, or, as it would seem in some cases, germicidal properties, the 
bodies of the dead microbes must at last be got rid of by phagocytosis, 
and some recent observations would seem to indicate that the useful 
elements of the serum may be, in part at least, derived from the digestive 
juices of the phagocytes. If ever there was a romantic chapter in 
pathology, it has surely been that of the story of phagocytosis. 
