160 BACTERIA IN RELATION TO DISEASE 



more ' virulent ' *. The nitrates can be concentrated by evaporation in 

 vacuo, and much more powerful toxic solutions obtained. By treatment 

 with alcohol or neutral salts, solid precipitates of still greater toxicity can 

 be gained. These precipitates contain of course a mixture of different sub- 

 stances, albumens and albumoses from the bouillon, and inorganic consti- 

 tuents besides the toxines. A complete isolation of the latter has not yet 

 been possible. They were formerly supposed to be proteid bodies (tox~ 

 albumines), but further purification has shown that they may possibly be of 

 simpler structure. They are extremely poisonous, one twenty-thousandth 

 part of a milligramme (= a0 uo 1 gram.) of a concentrated tetanus toxine 

 being sufficient to kill a mouse. For a human being 0-23 mg. would 

 probably suffice. 



The poisons contained within the bacteria (intracellular toxines) can 

 also be extracted. The best known example of these is Koch's tuber- 

 culin (143), a purified glycerine extract of tubercle bacilli. Pure toxines 

 have not yet been obtained by this method; the tuberculin of 1890 con- 

 tained, in addition to the unknown toxine albumens, albumoses and peptones 

 from the culture media. The newest tuberculin preparations too, Koch's 

 TR and TO, are extracts of dried and pounded bacilli from highly virulent 

 cultures. The finely pulverized bacilli are centrifuged in distilled water. 

 The first clear yellowish extract is the TO and has properties resembling 

 those of the old tuberculin. Repeated centrifuging of the sediment of 

 TO gives the more effective TR. Both TO and TR are mixed with 

 20 per cent, glycerine to assist their preservation. They are nothing but 

 virus-containing mixtures of all the soluble constituents of the tubercle 

 bacilli together with fragments of the crushed cells. 



Both the bouillon filtrates and the precipitated toxines retain their 

 virulence for a long time, but they are very sensitive to high temperatures 

 and alkalies or acids. Tetanus toxine is destroyed in a few minutes at 

 65° C, diphtheria toxine in two hours at 58° C. This instability, although 

 suggestive of the properties of enzymes, must not be regarded as indicating 

 a relationship of the two classes of compounds. 



Just as the poison of serpents or the alkaloids of poisonous plants are 

 the products of the vital activity of those organisms, so are the toxines 

 products of bacterial life. They are excreted from the bacterial cell during 

 life, and are poured into the culture fluids in abundance when the cells die ; 

 hence the great poisonousness of old cultures. As the microscope shows 

 us, too, that bacteria often become disintegrated in the tissues, they may 

 evidently contribute in this way also to the poisoning of the body. 



* Translator's note. These terms have been translated just as they stand in the German, where 

 the meaning is clear ; but they can scarcely be regarded as good English, unless the word virulent 

 is allowed to connote the power of multiplication possessed by the organisms. 



