SAPROGENS AND PATHOGENS 23 



tion of gases and by-products. (Fischer.) The reason for this is, 

 perhaps, to be found in the supposition that the bacteria abstract 

 oxygen for their own use, and thus cause the atoms to unite into an 

 entirely different substance.^ According to the above named inves- 

 tigator, it is notjpossible to express such chemical changes by a sim- 

 ple equation. J_Experiments have shown that B. typhosus and pyo- 

 cyaneus are able to split up olive oil or fat, and produce glycerine 

 and fatty acids, thus making them accessible to fermentation 

 (FischerO The action of the buttermilk organisms, while usually 

 very complex, may be represented by the following: 



lactose galactose dextrose 



C 6 H 12 O 6 =2C 3 H 6 O 3 



galactose lactic acid 



J $aprogens produce putrefaction which is the chemical trans- 

 formation of albuminous bodies with the evolution of nitrogen, and 

 of alkaloidal substances, known as ptomainesy Aromatic elements 

 are also produced, such asindol, phenol, kresol, etc. 



Pathogens.TJ^If the tissues are receptive to bacteria, and if the 

 latter, in any way, injure the tissues, then the invading organism is 

 called pathogenic^ (fRieoretically the tissues of the body are sterile. 

 But as a matter of fact, isolated pathogenic bacteria such as colon 

 and diphtheria bacilli, streptococci, and pneumococci, are often 

 found in the tissues and cavities of the body, and yet they cause 

 no pathogenic changes or symptoms. The blood during life is 

 sterile in health. ^ 



>/ Colon bacilli have been found encapsulated in the liver and 

 kidneys of nondiseased cadavers, shortly after death, which showed 

 that they had been there some time. Sixteen hours after death the 

 blood and tissues teem with bacteria that have wandered in from 

 the intestines. It has been shown that bacteria, even non-motile 

 ones, can migrate through the body during the agonal period. 7* 

 ^Bacteria may cause disease in several ways, mechanically: a 



