200 THE TOXINS PRODUCED BY BACTERIA 



When we take into account the extraordinary potency of these 

 poisons (in the case of tetanus the fatal dose of the pure poison 

 for a guinea-pig must often be less than '000001 grm.), we can 

 understand how attempts by present chemical methods to isolate 

 them in a pure condition are not likely to be successful, and of 

 their real nature we know nothing. Friedberger and Moreschi 

 have shown that the intravenous injection in the human subject 

 of a fraction of a loopful of a dead typhoid culture gives rise 

 to toxic symptoms, including marked febrile reaction. Such 

 injections are followed by the appearance of agglutinating and 

 bacteriolytic substances in the serum. These results show that 

 intracellular toxins may be comparable with extracellular toxins 

 so far as concerns the extremely small dose sufficient to produce 

 toxic effects. 



Amongst the properties of the extracellular toxins are 

 the following : They are apparently all uncrystallisable ; they 

 are soluble in water and they are dialysable ; they are pre- 

 cipitated along with proteids by concentrated alcohol, and also 

 by ammonium sulphate; if they are proteids they are either 

 albumoses or allied to the albumoses ; they are often relatively 

 unstable, having their toxicity diminished or destroyed by heat 

 (the degree of heat which is destructive varies much in different 

 cases), light, and by certain chemical agents. Their potency is 

 often altered in the precipitations practised to obtain them in 

 a pure br concentrated condition, but among the precipitants 

 ammonium sulphate has little if any harmful effect. Regarding 

 the toxins which are more intimately associated with the bacterial 

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

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

 easily 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 is set in an incubator at 37 C. over night. 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 vacua and stored in the dark, also in vacua, or in an exsiccator 

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

 dissolved up in a little normal saline solution. 



