[21] loc. cit. pp. 5, 6.
[22] Altmann's freezing process would be similar to the advance always insisted on by Ehrlich. It offers such great technical difficulties, however, that it has up to now been little used.
[23] The cause of these misunderstandings is the tinctorially different stages of development of the granules, as we have fully explained above. How little adequate tinctorial differences by themselves are to settle the chemical identity of a granulation, is at once evident on consideration of the granules of other organs. No one surely would assert, that a liver, muscle, or brain cell could occasionally secrete trypsin, simply because the granules of the pancreas stain similarly and analogously to those of the cells mentioned. We would here expressly insist that we only assume a distinct character for each kind of granulation, in the strict sense of the term for the cells of the blood, since they possess a relatively simple function. In very complex glandular cells, however, with various simultaneous functions, several kinds of granules may be contained.
[24] From a paper of Calleja we learn that Ramon y Cajal recognised the halos of the mast cells, and interpreted them in the manner we have above. Calleja also describes these halos and the method of demonstrating them in detail (thionin staining, and mounting the sections in glycerine). We must mention, however, that we do not consider this method suitable for the recognition of preformed halos, for the reasons above mentioned.
IV. LEUCOCYTOSIS.
The problem of leucocytosis is one of the most keenly debated questions of modern medicine. An exhaustive account of the various works devoted to it, of the methods and results, could fill by itself a whole volume, and would widely exceed the limits of an account of the histology of the blood. We can only deal fully therefore with the purely hæmatological side of the subject.
Virchow designated by the name "Leucocytosis," a transient increase in the number of the leucocytes in the blood; and taught that it occurred in many physiological and pathological conditions. In the period that followed particular attention was paid to the leucocytosis in infectious diseases, and to the investigators of the last 15 years in this province we owe very important conclusions as to the biological meaning of this symptom. Above all Metschnikoff has done pioneer service in this direction by his theory of phagocytes, and though his theory has been shaken in many essential points, yet it has exercised a stimulating and fruitful influence on the whole field of investigation.
To sketch Metschnikoff's doctrine in a few strokes is only possible by a paraphrase of the very pregnant words "Phagocytes, digestive cells." These words express the view, that the leucocytes defend the organism against bacteria by imprisoning them by the aid of their pseudopodia, taking them up into their substance, and so depriving them of the power of external influence. The issue of an infectious disease would chiefly depend on whether the number of leucocytes in the blood is sufficient for this purpose.