THE NATURE OF TOXINS 195 



plasm we know much less, but it is probable that, chemically, 

 their nature is similar, though some of them at least are not so 

 ra-ily injured by heat, e.g. those of the tubercle 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 extra- 

 cellular toxins : 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 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 vocno and stored in the dark, also in, vacuo, or in an exsiccator 

 < nntaining strong sulphuric acid. For use the contents of one are 

 dissolved up in a little normal saline solution. 



The comparison of the action of bacteria in the tissues in 

 the production of these toxins to what takes place in the gastric 

 digestion,, has raised the question of the possibility of the elabora- 

 tion by these bacteria of ferments by which the process may 

 be started. Thus Sidney Martin puts forward the view that 

 ferments may be produced which we may look on as the 

 primary toxic agents, and which act by digesting surrounding 

 material and producing albumoses these poisons being, as it 

 were, secondary poisons. Hitherto all attempts at the isolation 

 of bacterial ferments of such a nature have failed. 



But apart from the fact that with such bacteria as those of 

 tetanus and diphtheria, a digestive action may occur, analogies have 

 In-en drawn between ferment and toxic action. The chief facts 

 upon which such analogies have been founded are as follows : 

 Thus the toxic products of these and other bacteria lose their 

 tuxicity by exposure to a temperature which puts an end to the 

 activity of such an undoubted ferment as that of the gastric 

 juice. If a bouillon containing diphtheria toxin be heated at 

 G5 C. for one hour, it is found to have lost much of its toxic 

 effect, and in the case of b. tetani all the toxicity is lost by 

 exposure at this temperature. In both diseases there is a still 

 further fact which is adduced in favour of the toxic substances 

 1 icing of the nature of ferments, namely, the existence of a 

 driinitr period of incubation between the injection of the toxic 

 bodies and the appearance of symptoms. This may be inter- 

 preted as showing that after the introduction of, say, a f filtered 



