B. A second change that we find in the red blood corpuscles of the anæmias, is =poikilocytosis=.
By this name a change of the blood is denoted, where along with normal red blood corpuscles, larger, smaller and minute red elements are found in greater or less number. The excessively large cells are found in pernicious anæmia, as Laache first observed, and as has since been generally confirmed. On the contrary in all other severe or moderate anæmic conditions, the red corpuscles shew a diminution in volume, and in their amount of hæmoglobin. This contradiction, which Laache first mentioned, but was unable to explain, has found a satisfactory solution in Ehrlich's researches on the nucleated precursors of the myelocytes and normocytes (see below).
The blood picture of the anæmias is made still more complicated in that the diminutive cells do not preserve their normal shape, but assume the well-known irregular forms: pear-, balloon-, saucer-, canoe-shapes. Nevertheless in good dry preparations the smallest forms usually still shew the central depression. The so-called "microcytes" constitute an exception to this statement. These are small round forms, to which was allotted in the early days of the microscopic investigation of the blood, a special significance for the severe anæmias. They are however nothing but contraction forms of the poikilocytes, as the crenated are of the normal corpuscles. Consequently microcytes are but seldom found in dried specimens, whilst in wet preparations they are easily seen after some time. It is further of importance to know, that in fresh blood the poikilocytes exhibit certain movements, which have already given rise to mistakes in many ways. Thus at one time the poikilocytes were considered to be the cause of malaria. More recently the somewhat larger sizes were regarded by Klebs, Perles as amoebæ and similar organisms. In agreement with Hayem, who from the very first described these forms as =pseudo-parasites=, a warning must be given against attributing a parasitic character to them.
The origin of poikilocytosis, previously the subject of much discussion, is now generally explained in Ehrlich's way. For the mere fact, that by careful heating, poikilocytosis can be experimentally produced in any blood, forces one to the assumption that the poikilocytes are products of a fragmentation of the red blood corpuscles ("schistocytes," Ehrlich). And correspondingly the smallest fragments shew the biconcave form in the dry specimen; for they too contain the specific protoplasm of the disc "which possesses the inherent tendency to assume the typical biconcave form in a state of equilibrium."