THEORIES OF IMMUNITY. 



groups of cells. Therefore it happens that the 

 toxic substances are brought into existence out- 

 side of the cells, or at any rate can be separated 

 from the bacterial cells with ease, and may go 

 on producing their results after the bacteria 

 themselves have disappeared. In cultures, also, 

 the filtrates are found to contain the poisonous 

 products, whose action can be studied in such 

 filtrates, whilst the residue, consisting of the 

 bodies of the bacteria, is found to have very 

 little or no poisonous action whatever. The 

 actual constitution of these poisonous products 

 is not known, in spite of all the work done upon 

 them, but they are examples of extra-cellular 

 toxines, and they have the common property of 

 being precipitated by agents that also precipitate 

 the intermediate products of ordinary digestion — 

 the albumoses, — a fact that is of interest, for it 

 is possible that these toxic bodies may not be 

 far removed in composition from those that under 

 normal conditions form the food of certain of 

 the tissue cells. 



Bacteria which grow in this way more or less 

 locally and produce their effects most promi- 



42 



