190 THE TOXINS PRODUCED BY BACTERIA 



bacillus, already mentioned. In the case of all toxins the fatal 

 dose for an animal varies with the species, body weight, age, 

 and previous conditions as to food, temperature, etc. In 

 estimating the minimal lethal dose of a toxin these factors must 

 be carefully considered. 



The following is the best method of obtaining concentrated exotoxins : 

 The toxic fluid is placed in a shallow dish, and ammonium sulphate 

 crystals are well stirred in till no more dissolve. Fresh crystals to form 

 a bulk nearly equal to that of the whole fluid are added, and the dish 

 is set in an incubator at 37° C. overnight. Next day a brown scum 

 of precipitate will be found floating on the surface. This contains the 

 toxin. It is skimmed off with a spoon, placed in watch-glasses ; these 

 are dried in vacuo and stored in the dark, also in vacno, or in an exsiccator 

 containing strong sulphuric acid. For use the contents of one are 

 dissolved up in a little normal saline solution. 



The whole question of the parts played by toxins in bacterial 

 action is manifestly very complex. On the one hand, we have 

 a few processes, for example, diphtheria and tetanus, in which 

 very characteristic effects are produced on special tissues, by 

 soluble toxins. On the other hand, we have the great mass of 

 bacterial infections, in which the toxic effects are of a non-specific 

 character, in the sense that they are not the result of an action 

 on any particular tissue in the body, but on the vital processes 

 of the organism as a whole. There is thus the possibility that 

 with any one species of organism different effects may be pro- 

 duced by, it may be, different elements in the protoplasm of the 

 invading bacterial cell. Some of these elements may act on 

 such specialised body cells as those of the nervous system, liver, 

 or kidneys, giving rise to disturbances of metabolism. Other 

 poisonous elements may mainly act on the defensive cells of the 

 body, e.g., the leucocytes. A small dose of toxin may stimulate 

 these cells to an activity which results in the infection being 

 thrown off, either by the poison being neutralised, or by the 

 supply of toxin being cut off by the killing of the bacterium 

 producing it. A large dose of such a toxin, may, on the other 

 hand, altogether break down the defensive mechanism of the 

 invaded body. Even in such an apparently simple case as 

 diphtheria there is a complexity as the bacteria give rise to a local 

 inflammation and to a general toxsemia initiated by the specific 

 toxin. 



There is another point which must be kept in view, namely, 

 that some of the phenomena which have been regarded as 

 dependent upon the activity of bacterial toxins may possibly 

 be related to the little-understood process of anaphylaxis (see 



