Bacteriemia now is recognized readily by means of blood cultures and a blood culture in febrile patients has come to be a not unusual routine in many hospitals. The technic is so simple that it may be successfully done at the bedside in private practice and the culture media may be transported a considerable distance to the laboratory. With a sharp hypodermic needle the blood may be withdrawn from a prominent subcutaneous vein without noteworthy pain or danger. The blood culture enables one to recognize more readily the infectious character of the disease. With an infection proved, the interpretation of the physical and clinical phenomena becomes rational. On this a definite diagnosis may be made and the prognosis becomes more certain. The treatment necessarily becomes more definite, rational and conclusive. Before the use of blood cultures infectious endocarditis, termed malignant, ulcerative, etc., was sometimes recognized during life