On May 7, 1915, the Prussian Guards had passed over the railway at Krosno, and at night fell upon the Russian lines east of the Wistok. Particularly fierce encounters took place near Odrzykon and Korczina, ten to fourteen miles southeast of Frysztak. A little farther westward Van Mackensen delivered his main attack against the railway crossing at Jaslo, which fell on the same day, May 7. The Russians retreated in confusion with Von Mackensen close upon their heels. The whole defense on the Wisloka collapsed, and nothing apparently could now save the Dukla and those troops struggling through to escape from the net that was gradually being tightened around them. Meanwhile, General Ewarts's Army of the Nida, which formed the connecting link between the Russian northern and southern armies, had fallen back above Tarnow to the River Czarna in order to keep in touch and conformity with Dmitrieff's shrinking line, which was now actually broken by the Wisloka failure. The Russian position was extremely critical, for it seemed that the German general would roll up the two halves and thereby inflict a crushing and decisive defeat. General Ivanoff appears to have recognized Van Mackensen's intentions in time to devise measures to counteract the peril and save his left (Brussilov's army) from disaster. By pushing forward strong columns from Sanok on the Upper San to impose a temporary check upon the advancing tide, he gained a brief respite for the troops entangled in the passes. To that sector we will now turn to review the course of events.