THE NATURE OF TOXINS. 175 



the nature of which is unknown. It has also been found that the 

 bacteria of tubercle, tetanus, diphtheria, and cholera can pro- 

 duce toxins when growing in proteid-free fluids. In the case of 

 diphtheria, when the toxin is produced in such a fluid a proteid 

 reaction appears. Of course this need not necessarily be 

 caused by the toxin. Further investigation is here required, for 

 Uschinsky, applying Brieger and Boer's method to a toxin so 

 produced, states that the toxin body is not precipitated by zinc 

 salts, but remains free in the medium. If the toxins are really 

 non-proteid they may, on the one hand, be the final product of 

 a digestive action, or they may be the manifestation of a separate 

 vital activity on the part of the bacteria. On the latter theory 

 the toxicity of the toxalbumins of Brieger and Fraenkel, and of 

 the toxic albumoses of Martin, may be due to the precipitation 

 of the true toxins along with these other bodies. From the 

 chemical standpoint this is quite possible. 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 .00000 1 gr.), we must realise that all 

 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. Amongst the properties of the extracellular 

 toxins, however, are the following : They are certainly all un- 

 crystallisable ; they are soluble in water and they are dialysable ; 

 they are precipitated 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 relatively un- 

 stable, 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 

 or 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 cell we 

 know much less, but it is probable that their nature is similar, 

 though some of them at least are not so easily injured by 

 heat, e.g. in the case of the tubercle bacilli already mentioned. 

 In the case of all toxins the fatal dose for an animal varies 

 directly with the species, body weight, age, and previous con- 

 ditions as to, e.g., food, temperature, etc. In estimating the 



