THE PHENOMENON OF AGGLUTINATION 221 



avoided, since the normal agglutinating power of human beings is 

 never such that typhoid bacilli will be clumped by it in these dilu- 

 tions within one hour. Prompt clumping in serum dilutions of 1-20 

 is fairly reliable, but does not absolutely exclude an unusually high 

 normal agglutinating power. In carrying out tests clinically dilu- 

 tions of 1-20, 1-40, and 1-80 are usually made and observed for one 

 hour. From such tests diagnosis can be made without danger of 

 error. In rare cases of icterus the agglutinating power for typhoid 

 bacilli may be increased. Just what is the cause of this is not cer- 

 tain ; Wood 8 reports cases in which agglutination of 1-40 was pres- 

 ent with slight jaundice (hepatic cirrhosis). On the other hand he 

 has frequently failed to notice agglutination in other cases of intense 

 jaundice. It is not impossible, as Wood suggests, that the occasional 

 presence of unusual agglutinating power -in individuals with jaun- 

 dice has some relation to the frequent persistence of typhoid bacilli 

 in the gall bladder. 



Occasionally it will be noticed that dilutions of the patient's 

 serum of 1-5 to 1-20 fail to agglutinate, while higher dilutions will 

 give positive tests. This is referable to the so-called "pro-agglu- 

 tinoid zone," the principles underlying which we shall discuss in an- 

 other place. 



The Widal test in typhoid cases rarely appears before the end 

 of the first week, and, in the majority of cases, is present before the 

 end of the second week. It may proceed for months, although Wood 

 states that he has seen it disappear at the end of three to six weeks. 



In paratyphoid fever the diagnosis can often be made by agglu- 

 tination, and in dysentery, as we have seen, the fact that the pa- 

 tient's blood agglutinated the bacteria was one of the important facts 

 utilized by Shiga in his discovery of the organism which bears his 

 name. 



In pneumonia agglutination of the pneumococcus, isolated from 

 the patient's sputum by sera prepared by immunization with various 

 types of pneumococci, has become of considerable importance clin- 

 ically, since Neufeld and Haendel and, in this country, Cole, Dochez, 

 and Gillespie have determined that there are a number of different 

 types of this micro-organism. The use of pneumococcus serum in the 

 disease will be of value only if a serum is used which has been pro- 

 duced with an organism of the same type as the one infecting the 

 patient. Therefore, determinations of the type by highly potent 

 agglutinating sera give a finger-point to the variety of serum to be 

 used. Whatever may be the eventual outcome of the serum treat- 

 ment in pneumonia, no results whatever can be expected, according 

 to our present knowledge, unless such determinations are made. The 

 technique of agglutinations in pneumococcus work is facilitated by 



8 Wood. "Chemical and Microscopical Diagnosis," Appleton & Co., p. 242. 



