On 8th July Divisional headquarters moved to a camp in rear of the trench area, and the G.O.C. 51st Division took over command of the line. While the 152nd and 153rd Brigades were carrying out their tour-of duty in the line, little change in the situation took place, beyond the introduction of mustard-gas by the enemy. This was the most diabolical form of gas produced during the war. Death from its fumes was a prolonged agony ending in suffocation. Post-mortem examinations of its victims revealed the fact that all their organs from the throat to the abdomen were ulcerated throughout. The health of men who survived its effects was often permanently impaired, while externally, particularly in those portions of the body where perspiration is most profuse, the gas raised large blisters, which gradually chafed into open sores. Fortunately, the British mask was found to be absolutely proof against the effects of this gas. It was, however, found to be most persistent in its effects; the liquid contained in the shells became absorbed in the earth and continued vaporising for many hours. As a result, men who were working or living in an area that had been gas-shelled were often infected by the fumes many hours after the shelling had subsided. In some Divisions in the Ypres sector casualties from mustard-gas reached alarming proportions. After the 154th Brigade had taken over the line, the character of the enemy's activity changed for the worse. He continued his constant bombardments of the canal bank, and at the same time persistently shelled the forward area, no doubt in the hope that he might knock out any attack that was impending by overwhelming the troops with shell-fire in their assembly trenches. Some of those bombardments were of great violence, on one occasion 200 trench-mortar bombs being fired into the trenches on one battalion front.