Abstract
An agar gel precipitin test, using osmophoresis, has been devised for use with weakly reacting sera. The test was applied to various categories of sera, including sera from cases of farmer's lung which had reacted with a conventional immuno-diffusion test, and others which had not. All the conventionally sero-positive sera reacted positively in the new test as did nine of 16 cases in the sero-negative group. Concentration of sera in the latter group resulted in 11 positive tests out of a possible 12. Evidence was obtained of qualitative differences in the sera of these two groups. Unexpected reactivity with sera from cases of farmer's lung was found in a dialysate from a broth culture of T. polyspora. No reactions with this dialysate were obtained with the sera of any patients who did not have symptoms of farmer's lung.