II. ON THE PLACES OF ORIGIN OF THE WHITE BLOOD CORPUSCLES.
For the comprehension of the histology of the blood as a whole, it is of great importance to obtain an exact knowledge how and to what extent the three organs, which are undoubtedly very closely connected with the blood, lymphatic glands, bone-marrow, and spleen, contribute to its formation. The most direct way of deciding the question experimentally by excision of the organs in question, is unfortunately only available for the spleen. The part played by the lymphatic glands and bone-marrow, whose exclusion _in toto_ is not possible, must mainly be determined by anatomical and clinical considerations. But only by a careful combination of experiments on animals, of anatomical investigations, and especially, of clinical observations on a large scale, can light be thrown on these very difficult questions. It cannot be emphasised sufficiently how important it is that everyone engaging in hæmatological work should first of all collect a large series of general observations; otherwise errors are bound to occur. For instance, the endeavour is often made to compensate the lack of personal experience by careful literary studies; but in this way the histology of the blood falls into a vicious circle, of which the new phase of blood histology affords many examples. And it is characteristic of this kind of work that from the investigation of a single rare case, most far-reaching conclusions on the general pathology of the blood are at once drawn; _e.g._ Troje's paper, in which having failed to recognise the lymphocytic character of a case of leukæmia, and believing therefore that he had to do with a myelogenous leukæmia, the author denied and completely reversed all that had been previously established about this disease. It is equally hard to avoid errors if one confines oneself exclusively to animal experiments, without supplementing these by clinical experience, as is shewn by the numerous papers of Uskoff. Not the anatomist, not the physiologist, but only the clinician is in the position to discuss these problems.
In the introduction to this chapter we have already alluded to the striking retrograde movement in hæmatology at the present time, brought about by the view that the white corpuscles as a whole are derived from the lymphocytes. If we disregard the embryological investigations on this point (Saxer), anatomists, physiologists, and clinicians alike have taken up a similar point of view. Among anatomical papers we may refer to those of Gulland, according to whom all varieties of leucocytes are but different stages of development of one and the same element. He distinguishes hyaline, acidophil and basophil cells, and derives all from the lymphocytes. Arnold advocates similar views, though in a negative form. He says that a distinction between so-called lymphocytes and the leucocytes with polymorphous nuclei, on the grounds of the form of the cell and nature of the nucleus, is not possible at the present time. Neither is a classification based on the granules admissible, since the same granules occur in different cells, and different granules in the same cell. The work of Gulland and Arnold takes into consideration the differential staining of the granules in various ways. In spite of their facts we disagree with their conclusions; and we shall therefore have to analyse them in the special description of the granulated cells and granules.