176 INFECTIONS OF THE DIGESTIVE TRACT 



depend in part on an antitoxic action, which is perhaps 

 mainly anti-aggressive. It seems clear that if the solu- 

 ble poisons formed by the dysentery bacilli in the body 

 could be promptly neutralized, the bacilli would soon 

 fall a prey to the natural bactericidal process of the 

 serum and leucocytes. It is reasonable to believe that 

 sera may yet be obtained which will better fulfill this 

 need than do those at present in use. It must, however, 

 be clearly stated that even a powerful antitoxic or anti- 

 aggressive serum could not be counted upon to cure all 

 cases of dysentery, for in this disease there is in many 

 subjects a period when other bacteria than the bacilli of 

 dysentery (especially streptococci) enter the field of 

 action in a significant manner. A secondary infection 

 of mixed character is then set up, and against this the 

 specific sera of dysentery must necessarily be ineffective. 

 Finally it may be mentioned that there is sometimes 

 a therapeutic difficulty of a wholly different character, 

 due to the fact that a serum prepared with one strain 

 of dysentery bacillus is apt to be effective only for this 

 strain and to have little action on other varieties of the 

 bacillus. A serum may thus be worthless in a given 

 case because it is not adapted to the variety which is 

 acting. Shiga has recently proposed the use of a 

 universal or polyvalent serum designed to forestall 

 embarrassments of this sort. Shiga's advice is as fol- 

 lows. Two horses should be simultaneously immunized, 

 one with the bacilli of Shiga's types I and II, the 

 other with the bacilli of types I and IV. As soon as 

 a high grade of immunity is attained serum should be 



