VITAL PHENOMENA <>F BACTERIA 93 



Among the properties of the extracellular toxins are the following: 

 They are, so far as known, uncrvstallizable, and thus differ fromptomains; 

 they are soluble in water and they are dialyzable; 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 unstable, having their toxicity dimin- 

 ished or destroyed by heat (the degree of heat, etc., which is destructive 

 varies much in different cases). Their potency is often altered in the 

 precipitations practised to obtain them in a pure or concentrated condi- 

 tion, but among the precipitants ammonium sulphate has little if any 

 harmful effect. Regarding the intracellular 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 product 

 of tubercle bacilli. In the case of all toxins the fatal dose for an 

 animal varies directly with the species, body weight, age, and previous 

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

 minimal lethal dose of a toxin these factors must be carefully con- 

 sidered. 



The following is the method usually employed for obtaining concen- 

 trated extracellular toxins. The toxic fluid is placed in a shallow dish, 

 and ammonium sulphate crystals are well stirred in till no more dis- 

 solve. 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. (98.6 F.) 

 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, and these are dried in vacuo and stored 

 in the dark, also in vacuo, or in an exsiccator containing strong sul- 

 phuric acid. For use, the contents of one are dissolved in a little 

 normal saline solution. 



The comparison of the action of bacteria in the tissues in the pro- 

 duction of these toxins to what takes place in the gastric digestion, has 

 raised the question of the possibility of the elaboration by these bac- 

 teria of ferments, by which the process may be started. It would not 

 be prudent to dogmatize as to whether the toxins do or do not belong 

 to such an ill-defined group of substances as the ferments. It may be 

 pointed out, however, that the essential concept of a ferment is that of 

 a body w r hich can originate change without itself being changed, and 

 no evidence has been adduced that toxins fulfil this condition. Another 

 property of ferments is that, so long as the products of fermentation 

 are removed, the action of a given amount of ferment is indefinite. 

 Again, in the case of toxins no evidence of such an occurrence has been 

 found. A certain amount of a toxin is always associated with a given 

 amount of disease effect, though a process of elimination of waste 

 products must be all the time going on in the animal's body. Again, too 

 much importance must not be attached to loss of toxicity by toxins at 

 relatively low temperatures. Many proteids show a tendency to change 

 at such temperatures; for instance, if egg albumen be kept long enough 



