The evidence hitherto reported concerning the filtration of trachomatous material, and inoculation of man and monkeys with the filtrates points to the conclusion that the incitant of trachoma is not, as a rule, filtrable. Our findings confirm this view and indicate further that no virus causing the disease is adsorbed to Bacterium granulosis. On the other hand, Bacterium granulosis itself in heavy suspensions is irregularly filtrable through Berkefeld V candles, like some other bacteria (14), but it is present in the filtrates in only small numbers. When suspensions were used of trachomatous human and monkey tissues, which contain much fewer organisms than do actual cultures, Bacterium granulosis was never recovered from the filtrates.
The conception that trachoma is a disease caused by an ultramicroscopic virus is based on (a) the positive results of filtration in two animals, as reported by Nicolle and his coworkers, and (b) the presence of so called "inclusion bodies" in some of the cells of the lesions. One can state definitely that the evidence is now greatly against the filtrability of the etiological agent of trachoma. Furthermore, filtrability does not in itself suffice for the classification of an agent as an ultramicroscopic virus. Concerning (b), a vast literature has accumulated which indicates that the "inclusion bodies" of trachoma are not specific for the disease and that the bodies themselves may be bacterial in origin (15). We have not as yet found bodies of the kind characteristic of many filtrable viruses in the tissues of man or of monkeys with the experimental disease.