Hygienists will find material for thought in Pfannenstiel's1 recent report of the effect of wartime conditions on the general level of immunity among people of western Europe. For a decade Pfannenstiel and his co-workers have studied the variation in the bacteriostatic and bactericidal power of the blood of animals under variable nutritional and environmental conditions.
While they did not assume that variations in serum titer are complete measures of changes of immunity in experimental animals, they did assume that humoral variations are the best available indexes in such studies. The technic adopted for such studies was a modification of the technic endorsed by Wright and Holsen,2 a constant volume of defibrinated blood mixed with an arbitrary volume of bacterial suspension. The mixture is incubated for twenty-four hours with a control utilizing the same bacterial suspension in melted agar. Comparison of the number of colonies which develop in the