The first task therefore of a scientific treatment of the anaemic condition is carefully to define its extent. For this purpose the symptoms above mentioned are little suited, however great, in their proper place, their practical importance may be. Etymologically the word "=anaemia=" signifies a want of the normal =quantity of blood=. This may be "general" and affect the whole organism; or "local" and limited to a particular region or a single organ. The local anaemias we can at once exclude from our consideration. _A priori_, the amount of blood may be subnormal in two senses, quantitative and qualitative. We may have a diminution of the amount of blood--"=Oligaemia=." Deterioration of the quality of the blood may be quite independent of the amount of blood, and must primarily express itself in a diminution of the physiologically important constituents. Hence we distinguish the following chief types of alteration of the blood; (1) diminution of the amount of Haemoglobin (=Oligochromaemia=), and (2) diminution of the number of red blood corpuscles (=Oligocythaemia=). We regard as anaemic all conditions of the blood where a diminution of the amount of haemoglobin can be recognised; in by far the greater number of cases, if not in all, Oligaemia and Oligocythaemia to a greater or less extent occur simultaneously. The most important methods of clinical haematology bear directly or indirectly on the recognition of these conditions. There is at present no method of ESTIMATION OF THE TOTAL QUANTITY OF THE BLOOD which can be used clinically. We rely to a certain extent on the observation of the already mentioned symptoms of redness or pallor of the skin and mucous membranes. To a large degree these depend upon the composition of the blood, and not upon the fulness of the peripheral vessels. If we take the latter as a measure of the total amount of blood, isolated vessels, visible to the naked eye, _e.g._ those of the sclerotic, may be observed. Most suitable is the ophthalmoscopic examination of the width of the vessels at the back of the eye. Raehlmann has shewn that in 60% of the cases of chronic anaemia, in which the skin and mucous membranes are very white, there is hyperaemia of the retina--which is evidence that in such cases the circulating blood is pale in colour, but certainly not less in quantity than normally. The condition of the pulse is an important indication of diminution of the quantity of the blood, though only when it is marked. It presents a peculiar smallness and feebleness in all cases of severe oligaemia.