Ultrafiltration Experiments with the Viruses of Laryngotracheitis and Coryza of Chickens.

Ultrafiltration experiments with laryngotracheitis virus were. first reported by Beach (1930), Gibbs (1931) and Beach (1931). These investigators used the porcelain filters of Berkefeld and the fibrous filters of Seitz and agreed that the virus particles passed readily through the Berkefeld V filters, occasionally through the Berkefeld N filters, and were completely retained by the Berkefeld W filters using water pressure systems. There was some disagreement over the Seitz filtration experiments. Beach did not find sufficient virus in his ultrafiltrates to infect susceptible chickens, while Gibbs thought these filters superior to Berkefeld N filters, but not as consistent in results as the Berkefeld V filters. Later Gibbs (1933) introduced hormone broth as a menstruum for the suspension of laryngotracheitis virus particles, according to the technique of Ward and Tang (1929), Ward (1929) and Tang (1930), and found some improvement in filtration, but the results were far from satisfactory because the mucous and tissue cells in the exudate were not removed. During centrifugalization some of the virus particles were apparently thrown down with the cellular debris, while finer particles still remained in suspension to plug the pores of the filters. The purification of suspensions of vaccine virus by adding dilute solutions of organic acids until the iso-electric point is