6 BACTERIOLOGY 



luminous in the dark (phosphorescence), in consequence of 

 the molecular activity of their protoplasm. 



Influence of bacteria on the tissues. — The influence which 

 bacteria exert on the tissue of the bodies of men and 

 animals depends both on the qualities of the bacteria and 

 on the nature of the tissue. The action of the pathogenic 

 bacteria is not alike in all animals, and those which are 

 insusceptible to certain bacteria are said to be immune in 

 their relation to those particular organisms. Animals, 

 however, which are commonly immune towards a patho- 

 genic micro-organism may, under altered conditions, lose 

 their immunity ; for example, the frog, although usually 

 immune to anthrax, becomes susceptible to it at a higher 

 temperature. 



The virulence of pathogenic bacteria may be diminished 

 by various factors, amongst which are included sojourn in 

 the body of immune animals, increased atmospheric pres- 

 sure, the action of higher degrees of temperature, the 

 influence of sunlight, &c. This weakening is dependent 

 on an alteration in the products of metabolism. 



Toxins, toxalbumins, and ptomains. — As products of 

 the metabolism of those bacteria which effect an entrance 

 into the body substances are formed, some of which exert 

 violent toxic action, and which are divided into toxins and 

 ptomains, or cadaveric alkaloids, and to these is ascribed 

 the action of the pathogenic bacteria in originating morbid 

 processes. The toxins are further subdivided into tox- 

 albumifis and proteins. 



Toxalbumins are albuminoid bodies formed during the 

 growth of the bacteria upon culture-media, especially in 

 bouillon. Their activity depends upon certain definite 

 degrees of temperature, and they decompose at the boiling- 

 point. Our knowledge of them is due to the researches of 

 Eoux, Yersin, Brieger, and C. Fraenkel. 



