The response of the thoracic lymphatics, including those within the lung and mediastinum, is observed in all stages of pneumonia. But in epidemic influenza the reaction was much more prompt, appearing in the early stages and rapidly developing tissue changes along the channels and in the lymph nodes. The lymph channels during the period of the early serous pneumonia became dilated and filled with fluid with relatively few cells. The stroma immediately surrounding became œdematous, so that in the gross specimen the connective tissue between the lobules of lung were sometimes easily seen as gray strands. At this time this tissue was not increased in quantity and did not project above the level of the cut lung. The fibrous tissue remained soft and pliable, but formed quite wide strands. When the pulmonary reaction became hemorrhagic, red blood cells, leucocytes and large mononuclears were found mixed with the fluid in the lymphatics. We had no way of determining the direction of the lymph flow from the pulmonary tissues, but it was assumed that as there was no excessive loss of serous fluid from the lung and the lymphatics beneath pleura into the chest cavities that the fluid was draining through the channels lying about the bronchi and vessels. The further evidence of the direction of flow was seen in the rapid and comparable responses which occurred in the lymph glands along these routes. The glands about the bronchi and at the hilus became enlarged, red and succulent. The glands were often two and one-half centimeters in diameter. Their capsule was thin and stretched and the gland was quite soft. Many of them when cut open were almost diffluent. This acute lymph hyperplasia occurred in 30 of our cases. It is impossible to indicate any particular type of infection as being responsible for these lymphatic lesions. The nature of the bacteria present in these 30 cases differed quite considerably: 25 showed influenza bacilli, 15 pneumococci, 18 streptococci, 8 M. catarrhalis and 17 staphylococci. In as much as the pulmonary reaction was fairly constant in certain characteristics in all of our cases, and as we believe that the influenza bacilli were the very important factor in these reactions, it would appear that the lymphatic responses are only a part of the general inflammation of the respiratory organs. Comparison can also be made of the character of the lymphatic changes with that occurring within the pulmonary tissues. The lymphatics were filled with fluid which dilated all the available sinuses; the lymph nodes were œdematous and within them the reaction often had numerous small hemorrhages.