290 BLOOD AND BLOOD EXAMINATION 



luted may cause agglutination; on the other hand^ the dilution should not 

 be too weak, as the agglutinating substances in some eases of enteric fever 

 are not present in very large amounts, and if the serum be too greatly diluted 

 they are inactive. It is best to begin with a dilution of one part of serum 

 to thirty parts of bouillon, and, if a positive reaction be obtained, it should 

 then be determined with how weak a dilution we can still secure a reaction. 

 In some cases, a positive reaction has been obtained even after concentrations 

 of 1-5,000. If the test gives a positive result with a high dilution, the 

 diagnosis of enteric fever is thereby assured, with the one limitation that the 

 serum may perhaps have received its agglutinating properties from a .typhoid 

 fever some time previously, even several years before. 



If, however, the result of the test is negative with a dilution of 1 : 30, it is 

 well to repeat it in the course of the disease, daily if possible. Frequently 

 it is noted that in the early course of the disease the serum, which at first 

 showed no reaction while diluted, gradually in slighter concentration betrays 

 the presence of agglutinating substance. But the diagnosis of enteric fever 

 cannot be excluded with certainty even in case of a continued negative result 

 of the reaction. The appearance of the reaction may be expected at the 

 earliest upon the eighth day of the disease.^ [Since it is impossible to fix in 

 any way — except arbitrarily — the first day of the disease, it is hard to make 

 any accurate statement about the earliest appearance of Widal's reaction. 

 At the time when patients first consult a physician, two-thirds of them show 

 a positive agglutination reaction in the blood, but in a few it is delayed as 

 late as the fifth or sixth week, or it may never appear. Over 95 per cent, of 

 cases, however, show a reaction at some time in the course of the disease. 

 Difllerent epidemics vary greatly in these points, some showing a large pro- 

 portion of early reactions, while in others physicians complain of the high 

 percentage of negative reactions in the earlier weeks of the disease. — Ed.] 



In view of the very valuable diagnostic success of serum diagnosis in 

 enteric fever, it may be readily understood that an attempt would be made 

 to reach the same results in other diseases, but, unfortunately, there has been 

 as yet no practical success. Endeavors specially directed to the recognition 

 of tuberculosis by its specific agglutinating reaction may be looked upon as 

 futile, since Robert Koch reached entirely negative results in this direction. 



IX. BACTERIOLOGICAL EXAMINATION 



The diagnosis and also the prognosis may, under some circumstances, be 

 helped by the bacteriological investigation of the blood. There are quite a 



1 Lately Prbscher {Centralbl. f. Bakteriologie, xxxi) has proposed a modification 

 which indicates a decided practical improvement. According to this it is particularly- 

 valuable that a typhoid bouillon may be utilized in which the bacilli have been killed 

 by the addition of one part of a forty per cent, formalin to 100 parts of bouillon. This 

 bouillon may be used for weeks without losing its agglutinating property. For the 

 action of the serum upon the bacilli Proscher allows from one to two hours at blood 

 heat; for viewing the serum bouillon mixture which is kept in a bowl we employ a 

 low power dry lens (about ^ enlargement). 



