238 ILLINOIS ACADEMY OF SCIENCE 
for several hours. This was substantiated by F. Cohn and 
Robert Koch, who also showed these resistant forms of micro 
organisms to be the spores of bacteria. In 1878 Robert Koch 
completed his brilliant experiments in the making of solid 
culture media. This enabled the scientific world to recover 
micro organisms from diseased animals by growing them on 
this media from the blood or secretions obtained from that 
animal, and to successfully study their morphology. Koch 
demonstrated that the changes which took place upon the con- 
tact of bacteria and media were those of decomposition, caused 
by bacteria. 
Pasteur, while engaged in research work along the lines of 
the silkworm disease, and anthrax in cattle for the French 
government, succeeded in proving that the etiology of these 
diseases was due to micro organisms. Later he found and 
reported the cause of chicken cholera, and by inoculation 
experiments told how to guard against them. Since the fun- 
damental work of Pasteur and Robert Koch, the studies of 
pathogenic micro organisms in general and of pathogenic 
bacteria in particular have been placed on a firm basis, and 
have assumed the greatest importance in the theory and prac- 
tice of medicine. The connection of bacteria with certain 
forms of disease was conclusively demonstrated by these men, 
although it had long been suspected that suppuration was 
due to the presence of organisms in wounds. 
That numerous small organisms scourged and ravaged the 
human body and that all people did not die during the epi- 
demics of disease proved that the body protected itself against 
disease; this fact was laid bare to the knowledge of the world 
by the famous Erlich in his theory of phagocytosis, and side 
chain theory. He proved that the extensive metabolism of 
the human body was endowed with the power of eating or 
feeding upon the micro organisms which invaded the body. 
This substance which accomplished this was called phagocytes, 
taken from the Greek, phagoto, eat, cyte, a cell, are classed to 
day as leukocytes or white blood corpuscles. They have at- 
tractive powers and can remove from the blood the bacteria 
and foreign bodies of invasions, in the same manner as iron 
filings are attracted toward a magnet: the iron filings being 
the disease producing bodies and the magnet, the leukocyte. 
This is shown by the attraction or repulsion that exists between 
