It is rather difficult to estimate the functional loss and the structural lesion that the human organism has received from an attack of any acute or chronic disease. The pathologist can describe the morbid anatomy in the dead patient, but the clinician has far more difficulty in estimating the clinical damage to the convalescent living patient. Diagnosis is the time consuming element in medicine: after diagnosis, treatment is easy and takes little time: but more difficult than either is this problem of the clinical damage to the individual. In malaria, for example, is the patient's functional power less, either in single organs or in the system as a whole? Will his structural pathology shorten his life? Is he a malaria carrier, and therefore, a clinical liability to the community? Are there parasites lurking in the trabeculae of the spleen and the sarcoplasm of the cardiac muscle ready to reproduce and cause the disease when the normal resistance is lowered below an unknown level?