RELATION OF SCIENCE TO HUMAN LIFE—SEDGWICK. 677 
in countless numbers in our alimentary canals, in short, that they 
are found everywhere on our body surfaces. How is it that they do 
not increase and turn our organs into a seething mass of putrefying 
corruption? One would expect that even if the skin and the mem- 
brane bounding the internal organs to which they obtain entrance 
incurred the slightest lesion, even a pin prick, that they would have 
been able to enter. We know that after death they at once obtain 
complete dominion, and we therefore infer that in life there must be 
some protective mechanism in the body capable of dealing with them. 
The discovery that there is such a mechanism was made in the 
early eighties by the distinguished Russian zoologist Elias Metschni-— 
koff, though the need of its existence was not recognized by biologists 
in general until later. The result of this was that his remarkable 
discoveries were at first pooh-poohed and discredited by many, but 
ultimately they gained acceptance, and their further development in 
his own hand and that of others has wrought a revolution in the art 
of preventive medicine. 
The mechanism consists of the small amceboid cells found in the 
blood, lymph, and body fluids generally, and called leucocytes, or 
white blood corpuscles. Though long known to exist, very little had 
been ascertained as to their function until Metschnikoff, working at 
such remote subjects as the embryology of sponges, the structure and 
digestion of polyps, the blood of water fleas, realized that these small 
amceba-like cells, which exist in all organisms, actually swallow, 
digest, and so destroy small foreign bodies which have invaded the 
organisms. He called them the phagocytes, and all his subsequent 
work has been directed to the elucidation of their mode of action. 
It is to Metschnikoff’s work, prompted solely by the scientific 
spirit, that we owe our knowledge of phagocytosis and the great 
theory of immunity which has proceeded from it. It is impossible 
at the present moment to estimate fully the value to man of Met- 
schnikofi’s discoveries. Suffice it to say that they have already led 
to important practical results, and have revolutionized treatment. 
I must now turn for a moment to another subject of the greatest 
importance to mankind, and one which has been brought into notice 
by the researches, perfectly useless so far as our material welfare is 
concerned, which were undertaken with the view of elucidating the 
great question of organic evolution. I refer to the study of genetics, 
which deals with the question mainly of the transmission of the 
properties of the organism; but it deals with even a larger subject 
than that. It looks into and tries to determine the laws which 
govern the origin of the characters of individuals, whether plants 
or animals, whether those characters have been acquired by inheri- 
tance or in some other way. The subject is of the utmost interest 
and practical importance to man from three points of view. It has 
