[nicholls] unsolved PROBLEMS OF LMMUNITY 263 



production of protective substances which, entering the blood stream, 

 are carried to the remotest parts of the body. These substances can 

 he demonstrated in the blood and are undoubtedly the result of some 

 vital process on the part of the infected organism, though where they 

 are formed has not as yet been determined with certainty. Farther, 

 it seems to be generally agreed that Ehrlich's view is correct, namely, 

 that before bacterial intoxication can occur, the toxin in question must 

 enter into a chemical combination with some cellular element of the 

 body. It is important to note in this connection that these chemical . 

 affinities vary considerably, certain toxins having a special predilection 

 for attacking certain cells, while others escape. Thus, the tetanus 

 toxin and that of rabies have a marked tendency to attack the central 

 nervous system; the diphtheria toxin has an attraction for the peri- 

 pheral nerves; the toxin of scarlatina is prone to damage the secreting 

 cells of the kidney, and so on. 



To emphasize this peculiarity that the toxin has of turning to a 

 particular class of cell, Wright has coined the term " tropine " to desig- 

 nate bodies of this kind. Adopting this terminology, we may call the 

 protective substances elaborated to combat the deleterious agents " anti- 

 tropincs.'' Several kinds of antitropines have been discovpred, some 

 capable of neutralizing the effects of bacterial tropines, others the 

 tropines of certain highly organized plants, still others, those of animal 

 origin, such as snake-venom. After twenty years of research we are 

 only now beginning to apprehend the importance of these antitropines 

 and the marvellous complexity of the protective forces of the body. 

 Several kinds of bacterial antitropines have already been demonstrated, 

 such as antitoxins, agglutinins, precipitins, lysins, and opsonins, and 

 there may be others. IVtoreover, these differ both quantitatively and 

 qualitatively in special cases. 



The work of Wright and Douglas, published during the past two 

 or three years, has thro^,vn a flood of light upon the abstruse subject 

 of immunity production. These observers have shown conclusively 

 tliat the blood-fluids play a most important role in connection with 

 phagocytosis. By investigating the action of the serum and the leuco- 

 cytes separately and in conjunction upon bacteria, they have demon- 

 strated that substances exist in the serum which, in some way later, 

 the microbes in such a way as to render them an easy prey for the 

 leucocytes. These substances they call •' opsonins," from the word 

 " opsone,'' " I cater for," " provide victuals for." Divesting their 

 method of sundry technical details, it may be summed up as follows: 

 Certain volumes of serum, bacterial emulsion, and leucocytes, pre- 

 viously washed in a half per cent solution of sodium citrate in normal 



