172 CHEMISTRY OF THE IMMUNITY REACTIONS 



proportions and groupings of the scanty number of amino-acids that 

 make up the protamines and histones of sperm to be characteristic 

 of the sperm of certain species and famihes. 



In the subsequent discussion of the various reactions of immunity 

 the subject of specificity will receive further consideration. Of these 

 reactions, one of the simplest and most studied is that of 



TOXINS AND ANTITOXINS 



In the preceding chapter on the bacteria and their products the 

 nature of the true toxins was defined, and attention was called to the 

 fact that one of their most important characteristics is that immuniza- 

 tion of animals against them leads to the accumulation in the blood 

 of substances capable of neutralizing their poisonous action. Such 

 true toxins are produced especially by the diphtheria bacillus and the 

 tetanus bacillus; also, but less strikingl}^, by B. pyocyaneus, B. botu- 

 linus, pathogenic gas bacilli, dysentery bacilli, and possibly by a few 

 others. In addition to these, numerous bacteria produce hemolytic 

 poisons w^hich seem to have properties similar to the toxins; and there 

 are also toxins produced b}^ plants (abrin, ricin, crotin, and mushroom 

 poisons) and by animals (snake venom, scorpion and spider toxin, and 

 eel serum). Against all of these, true antitoxins may be obtained by 

 the immunization of animals. 



Ehrlich's Conception of Toxins and Antitoxins. — According 

 to Ehrlich's theory, the action of toxins upon cells is purely ^hejuinaL 

 A toxin unites with a cell because some chemical grovip in the molecule 

 of toxin has a chemical affinity for some particular group in the cell 

 protoplasm. For convenience in description names have been given 

 to these groups; the group of the toxin that combines with the cell 

 has been called the haptophorous grouD, or haptophore, while the 

 group in the protoplasm that combines with the toxin is known as 

 the receptor.^^ It has been found that after being kept for some 

 time, or when placed under certain unfavorable conditions, the toxin 

 loses its poisonous properties without losing its power to combine 

 with cells, as shown by the fact that immunization with such altered 

 toxin gives rise to the formation of antitoxin. Therefore it is not the 

 haptophore that causes the harm to the cell, but there must be some 

 other groups with this particular function. To the group that pro- 

 duces the harm the name toxophorc is given. If all tlu> receptors of 

 a cell are coni])ined by toxin molecules that have lost their toxophore 



*^ Ehrlich has used certain diaKrams to illustrate these various groups and 

 their relations to the cells and to one another, which arc generally used in 

 exi)lairiiiig his thef)ry. From a teaching standpoint they have seemed to be 

 umicsiralilc, in that the student soon comes to ascril)e piiysical properties and 

 ai)i)caranc('s to what should he considered as oliemical coml)inations. The 

 toxopliorc grouj) Ix'comes "the hlack fringed end of the toxin." etc. To one 

 accustomed to thinking in chemical terms there is no diiiiculty in following the 

 literature and understanding the reactions as chemical reactions, which they are. 



