164 LOUIS PASTEUR 



All of this work lent strength to the hypothesis 

 that it is the germ that is the cause of the disease. 

 But it was possible for objectors still to urge that 

 it is not germs that cause disease, but something 

 that goes along with germs, a sort of virus that 

 may not appear in the fluid part of the blood, but 

 which may nevertheless be a product of the body. 

 The culture experiments of Koch could be inter- 

 preted as simply diluting this something without 

 getting rid of it. It was this problem to which 

 Pasteur in his studies on anthrax first directed his 

 attack, and he attacked the problem in a thorough- 

 going way that left no reasonable doubt as to the 

 issue between the two rival theories. He began by 

 making culture experiments using sterile urine in 

 which the bacillus of anthrax grows very well, and 

 also various other culture media. He inoculated a 

 relatively large amount of culture fluid with a drop 

 of blood from an animal with anthrax. The char- 

 acteristic bacteria of the disease were soon swarm- 

 ing throughout the culture medium. Then a drop 

 of this culture was introduced into a fresh lot of 

 fluid, and when this was teeming with bacteria, a 

 drop from the latter was introduced into a third 

 lot. If the first dilution is i to 1,000, the second 

 would be i to 1,000,000 and the third 1 to 



