238 PHARMACEUTICAL BACTERIOLOGY 



substances were of a specific character, each species or variety of disease 

 germ depending upon its specific materials found in the cell. It was sup- 

 posed that cell exhaustion for dysentery, for example, did not also result 

 in exhaustion for typhoid infection, or cholera infection, or tubercular 

 infection. Like (a) this also was mere theoretical or rather hypothetical 

 assumption and was without adequate scientific proof. 



c. Intoxication Theory. Toxic Destruction Theory. According to 

 this theory, the infecting agents (bacteria) were gradually checked in their 

 growth and finally destroyed by toxins or harmful agents which they them- 

 selves produced. As is known, the ordinary phenomenon of active 

 combustion (burning) results in the formation of substances actually em- 

 ployed in extinguishing fires, namely water and carbonic acid gas. In 

 a similar manner, so it was supposed, the harmful and destructive typhoid 

 infection (Bacillus typhosus), for example, formed certain gradually ac- 

 cumulating substances which were fatal to the continued existence of the 

 infecting agent itself. 



Many experiments and tests have been made, the results of which 

 apparently supported the theories (b) and (c) but the experimental evi- 

 dence as a whole were so faulty and inconclusive that as a result both 

 theories are now practically abandoned, giving way to the more recent 

 statement of immunity and immunizing agents. 



3. The History and Development of the Present Conception of 

 Immunity. 



i. General Statement of Immunology. In 1890 Behring and Kitasato 

 found that the cell-free blood (serum) of rabbits and of mice which had 

 been artificially immunized against tetanus, neutralized or destroyed the 

 toxic substances of the tetanus bacillus. To this substance they gave the 

 name antitoxin. This was an epoch-making discovery. It led to the 

 finding of other antitoxins or antibodies which are now used in the treat- 

 ment of disease as will be more fully explained in a subsequent chapter. 

 Antitoxins, like the toxins, possess many of the characters of albuminoids, 

 are quite readily decomposed and are incapable of isolation from the blood 

 or from the tissue cells. Never having been obtained in purity nothing is 

 known regarding their physical appearance. They are readily destroyed 

 at comparatively low temperatures (65 to 75 C.) and by exposure to 

 light and air. They are very sensitive to acids and are best preserved 

 by evaporating the blood sera in which they are contained to dryness in a 

 vacuum at a low temperature and storing in a vacuum, at a low tempera- 

 ture, away from light and in a dry place. Experimentally it has been dem- 

 onstrated that the antitoxins are intimately combined with the globulins 

 of the blood. This discovery led to the manufacture of .concentrated anti- 

 toxins by precipitating the globulins with ammonium sulphate, magnesium 



