SUMMARY 43 



groups from the coll and their action upon toxin molecules in the 

 circulation. 



Summary. To sum up: So far as our knowledge of the actual 

 aggressive forces of the invading bacteria are concerned we must 

 admit that, barring the morphological changes with which we have 

 become acquainted, and which we have come to look upon as pas- 

 sively aggressive forces, active forces furnished by the living organ- 

 isms during the infection have not been satisfactorily demonstrated. 

 But we have seen that bacterial decomposition products in them- 

 selves possess a certain infection-favoring influence and are in this 

 sense aggressive. That a decrease in the offensive forces of the host, 

 finally, is in a measure equivalent to an increased aggressivity of the 

 infecting bacteria is almost self-evident. These forces will be studied 

 in subsequent chapters, but before entering upon their consideration 

 it may not be out of place to briefly review our knowledge of those 

 products of bacterial activity or degeneration which play a role in 

 the production of the picture of the so-called infectious diseases and 

 their probable manner of action. 



