Bile is often referred to as if its chemical composition was constant and that by treating samples of bile with extractives similar results would be obtained, whereas samples of human bile differ to such an extent that the term bile in itself signifies little. Two samples of human bile may differ to such an extent that while one sample has the qualities of true bile as regards its bile salt content the other may be entirely devoid of lytic action on red blood cells. Numerous experiments made with human bile obtained during life and from the post mortem room have shown this to be correct. The actual bile salt content of bile can be judged by boiling the bile to remove much of the protein, and also to destroy bacterial activity and then contrast the haemolytic activity of the treated sample with a 1 per cent, solution of bile salt in normal saline.