Bingel A (1918). Über Behandlung der Diphtherie mit gewöhnlichem Pferdeserum [On the treatment of diphtheria with normal horse serum]. Deutsches Archiv für Klinische Medizin 125:284-332.
"I proceeded very cautiously. After I had treated some adult diphtheria patients with ordinary horse serum in 1911, I began in 1912 to treat alternate adult patients with antitoxin serum and with ordinary serum, exactly in the temporal sequence in which they were admitted to the ward. The children all received antitoxin serum. In the second half of the year 1912 and in the first half of 1913, I gradually lowered the age of those to be treated with ordinary horse serum, and from 1 July 1913 every second case was treated with ordinary horse serum, whether child or adult, regardless of the severity of the illness or the presence of complications. I note that it is absolutely inadmissible to compare the results for different time periods, for example to give antitoxin serum during one year, and then to give only ordinary horse serum during a second year, and then to compare the results. That would lead to seriously wrong conclusions, for in no infectious disease is the nature of the epidemic so changeable as in diphtheria. Mostly we see light epidemics, but quite serious ones still occur. I remind [the reader] of the heavy epidemics in Berlin and Hamburg of the year 1910, and the one in Leipzig of 1914, which recall the bad times of the period before serum. The table on p286-7 shows how many patients were treated in each year and the number of deaths."