416 BACTERIOLOGY. 



1. That infection may be considered as a contest 

 between bacteria and living tissues, conducted on the 

 part of the former by means of the poisonous products 

 of their growth, and resisted by the latter through the 

 agency of proteid bodies normally present in and 

 eliminated by their integral cells. 



2. That when infection occurs it may be explained 

 either bj'' the excess of vigor of the bacterial products 

 over the antidotal or protective proteids eliminated by 

 the tissues, or to some cause that has interfered with 

 the normal activity and production of these bodies. 



3. That immunity is most frequently seen to follow 

 the introduction into the body of the products of growth 

 of bacteria that in some way or other have been modified. 

 This modification may be artificially produced in the 

 products themselves of virulent organisms, and then 

 introduced into the tissues of the animal ; or the viru- 

 lent bacteria may be so treated that they are no longer 

 virulent, and when introduced into the body of the 

 animal will eliminate poisons of a much less vigorous 

 nature than would otherwise be the case. 



4. That immunity following the introduction of 

 bacterial products into the tissues is not in all cases the 

 result of the permanent presence of these substances, 

 per se, in the tissues, or to a tolerance acquired by the 

 tissues to them, but is probably, in certain instances, due 

 to the formation in the tissues of another body that acts 

 as a protecting antidote to the poisonous products of 

 invading organisms. 



5. That this protective proteid that is eliminated by 

 the cells of the tissues need not of necessity be antago- 

 nistic to the life of the invading organisms themselves, 



