"REACTIONS" AND SIMILAR PHENOMENA 317 



from the usual " accelerated effect " occurring in patients injected 

 with serum for the second time. The symptoms are rigor, 

 pyrexia, vomiting, rash, and collapse, whereas the effects which 

 develop in a day or two consist of rash, joint pains, and pyrexia. 



The precipitation theory is now generally abandoned, since 

 further investigation shows that there is no close parallelism 

 between the occurrence of the disease and the presence of 

 precipitins in the serum. Thus it is often found that the symptoms 

 are present when not the slightest trace of antihorse precipitin is 

 demonstrable. On the other hand, precipitins may occur when 

 the disease does not develop, though this is a fact of less impor- 

 tance, since it is necessary, on this theory, that the precipitin and 

 the unaltered horse serum should be present simultaneously, and 

 this latter fact is usually impossible of proof. But Widal and 

 Rostane have brought forward very strong negative evidence in 

 showing that the disease does not necessarily occur after the 

 intravenous injection of a powerful antihuman precipitating 

 serum in man. 



These arguments, though strong, cannot be regarded as entirely 

 conclusive. As regards the absence of the precipitin in some 

 cases of serum disease, it may be pointed out (a) that it may have 

 all been removed in the form of precipitum when the sample was 

 collected, and (b) that the demonstration in vitro of a minute 

 amount of precipitin is by no means easy, and requires an appro- 

 priate correlation between the precipitating and normal sera, or 

 the phenomenon may be missed. Further and this applies to the 

 negative experiments of Widal and Rostane we do not know 

 exactly what conditions are necessary to the union of precipitin 

 and antigen to form an insoluble precipitate, and whether these 

 are always present in vivo. Some experiments, it is true, appear 

 to show that the combination never occurs in the animal body, 

 but they are inconclusive, and the supposition is in the highest 

 degree unlikely. It appears probable that precipitation, like 

 agglutination, depends on the presence of certain salts, as well as 

 on that of the antibody and antigen, and it may be that these are 

 sometimes absent or not present in an available form. In this 

 connection we may quote the researches of Netter, which are of 

 great practical importance. He showed that the administration 

 of calcium lactate at the time of the injection, and for a day or 

 two after, caused a great diminution in the number of cases of the 

 serum disease. His results have been generally substantiated, 



