We regard as anæmic all conditions of the blood where a diminution of the amount of hæmoglobin can be recognised; in by far the greater number of cases, if not in all, Oligæmia and Oligocythæmia to a greater or less extent occur simultaneously.
The most important methods of clinical hæmatology 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. Ræhlmann has shewn that in 60% of the cases of chronic anæmia, in which the skin and mucous membranes are very white, there is hyperæmia 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 oligæmia.
The bleeding from fresh skin punctures gives a further criterion of the quantity of blood, within certain limits, but is modified by changes in the coagulability of the blood. Anyone who has made frequent blood examinations will have observed that in this respect extraordinary variations occur. In some cases scarcely a drop of blood can be obtained, while in others the blood flows freely. One will not err in assuming in the former case a diminution of the quantity of the blood.
The fulness of the peripheral vessels however is a sign of only relative value, for the amount of blood in the internal organs may be very different. The problem, how to estimate exactly, if possible mathematically, the quantity of blood in the body has always been recognised as important, and its solution would constitute a real advance. The methods which have so far been proposed for clinical purposes originate from Tarchanoff. He suggested that one may estimate the quantity of blood by comparing the numbers of the red blood corpuscles before and after copious sweating. Apart from various theoretical considerations this method is far too clumsy for practical purposes.