18 BACTERIAL PRODUCTS 



produced by the action of these poisons, notably congestion, 

 inflammation, and necrosis ; but the soluble poisons carried 

 in the blood-stream further develop general effects. Thus, 

 the anthrax bacilli cause local oedema and pustule, and 

 further lead to nervous collapse. The diphtheria bacillus 

 causes special throat lesions, while the toxin it develops, 

 circulating widely, impairs the functions of the great nerve- 

 centres. 



In all these reactions between toxins and the tissues or 

 enzymes and the tissues or the complex proteid bodies of 

 the tissues we appear to have a similar uniformity of type 

 of action. Whenever an animal is immunised against a 

 bacterium, against blood corpuscles, against a serum or 

 against enzymes and the like, an c antibody ' is formed 

 which possesses the peculiar property of linking itself on 

 to the substance that has been injected, and against which 

 the organism is now ' immunised.' This ' antibody ' sub- 

 stance, which has a variety of names but which we will 

 speak of as the immune body, may be produced in very 

 large quantities. It may, however, be present in minute 

 quantities in the blood of animals which have apparently 

 not been subjected to any special treatment. Such an 

 immune body is spoken of as being ' stable,' as it has the 

 power of resisting a comparatively high temperature over 

 a prolonged period. This stability, however, is not the same 

 in all cases. In the blood of the treated or infected animal 

 it is usually associated with a second substance, also variously 

 named, to which we will apply the term ' complement,' 

 the name by which it is now most generally known. This 

 complement is present in the blood of all animals, though 

 it varies in character in different species, and, so far as we 

 know, is not dependent upon the action of any specific 

 substance. Without the presence of this complement the 

 immune body appears incapable of combining with the 

 material by which it is produced. With the complement, 

 however, the combination readily takes place. This can 

 be proved very easily, for it has been found that the comple- 

 ment is what is called a ' labile ' substance, i.e. it is easily 

 and rapidly destroyed at a temperature of 60 C. Under 

 ordinary conditions the amount of this complement is not 



