THE WHITE BLOOD CORPUSCLES.
The physiological importance of the white blood corpuscles is so many sided that they form the most interesting chapter of the subject. That the white corpuscles play a significant part in the physiology and pathology of man has been recognised but slowly, obviously because there was at first some hesitancy in ascribing important functions to elements that are present in the blood in such relatively small numbers. A place in pathology was first assured to them by Virchow's discovery of leukæmia. The interest in the question was increased by Cohnheim's discovery that inflammation and suppuration are due to an emigration of the white blood corpuscles, and these conditions were particularly suitable for throwing light on normal processes. The fact that in diffuse inflammations, large quantities of pus are often produced in a short time, without the blood being thereby made poorer in leucocytes,—that the opposite indeed occurs,—necessitated the supposition that the source of the leucocytes must be extraordinarily productive. Hence in contradistinction to the red blood corpuscles, their small number is fully compensated by their exceptional power of regeneration.
Nevertheless, a considerable time elapsed before the powerful impulse that started from Cohnheim, bore fruit for clinical histology. As we have mentioned this was due to the circumstance that an exact differentiation of the various forms of leucocytes was very difficult with the methods in use up to that time. Although such distinguished observers as Wharton Jones and Max Schultze had been able to distinguish different types of leucocytes, Cohnheim's work remained clinically fruitless since the criteria they assigned were far too subtle for investigation at the bedside. Virchow indeed, the discoverer of leucocytosis, interpreted it as an increase of the lymphocytes; whereas it is chiefly produced by the polynuclear cells. Only after the distinction was facilitated by the dry preparation and the use of stains, did interest in the white corpuscles increase, and continue progressively to the present day. This is borne out by the exceptionally exhaustive hæmatological literature, and particularly by that of leucocytosis.
In spite of these advances, a retrograde movement in the doctrine of the leucocytes has gained ground surprisingly, especially in the last few years. Ever since Virchow's description of the lymphocytes, observers have tried to separate the various forms of leucocytes one from another, and if possible to assign different places of origin to these different kinds. There now suddenly appears an endeavour to bring all the white blood corpuscles into one class, and to regard the different forms as different stages merely of the same kind of cells. The following sections will show that this tendency is unwarranted and unpractical.
I. NORMAL AND PATHOLOGICAL HISTOLOGY OF THE WHITE BLOOD CORPUSCLES.
The classification of the white corpuscles of normal human blood, drawn up by Ehrlich, has been accepted by most authors, and we therefore give a short summary of it, as founded on the dry specimen.
1. The Lymphocytes. These are small cells, as a rule approximating in size to the red blood corpuscles. Their body is occupied by a large round homogeneously stained nucleus centrally situated, whilst the protoplasm surrounds the nucleus as a concentric border. Between nucleus and protoplasm there is often found a narrow areola, which doubtless results from artificial retraction. Nucleus and protoplasm are basophil, nevertheless in many methods of staining the protoplasm possesses a much stronger affinity for the basic stain than does the nucleus. The nucleus in these cases stands out as a bright spot from the deeply stained mass of protoplasm, which is reticulated in a peculiar manner.
Within the nucleus are often to be found one or two nucleoli with a relatively thick and deeply stained membrane. With methylene blue and similar dyes the protoplasm stains unequally, which is not to be considered as the expression of a granulation, as Ehrlich first assumed, but rather of a reticular structure. The contour of the lymphocytes is not quite smooth as a rule, at least in the larger forms, but is somewhat frayed, jagged, and uneven (Fig. 1). Small portions of the peripheral substance may repeatedly bud off, especially in the large forms, and circulate in the blood as free elements. In stained specimens, especially from lymphatic leukæmia, these forms, which completely resemble the protoplasm of the lymphocytes in their staining, may from their nature and origin be readily recognised.
As far as the further metamorphosis of the nucleus is concerned, a sharp notching of the border of the nucleus may occasionally be found, the further fate of which is shewn in the accompanying figure (Fig. 3). It is evident that in this case the resulting nuclear forms are quite different from those which are characteristic of the polynuclear elements.
The protoplasm possesses no special affinity for acid and neutral dyes, and hence in triacid and hæmatoxylin preparations the small lymphocytes are seen chiefly as lightly stained nuclei, apparently free. In the larger cells the protoplasm can be seen even in these preparations to be slightly stained. By the aid of the iodine-eosine method the reaction of the protoplasm of the lymphocytes is shewn to be strongly alkaline. They do not contain glycogen.
These properties taken as a whole constitute a picture completely characteristic of the lymphocytes; and these elements can thereby be diagnosed and separated from other forms, even when their size varies. Generally speaking, these cells, as above mentioned, are distinguished in the blood of the healthy adult by their small size, approximating to that of the red blood corpuscles. In the blood of children on the contrary larger forms are found even in health; and in lymphatic leukæmia particularly large forms occur, which are mistaken in various ways by unpractised observers. Thus Troje's "marrow cells" still figure in the literature, but have absolutely nothing to do with the marrow. They are large lymphocytes, as was established by A. Fränkel years afterwards.
Fig. 1.
Fraying out of the protoplasmic border in large lymphocytes. Free plasma elements formed by budding. ("Plasmolysis.")
(From a photograph of a preparation from chronic lymphatic leukæmia.)
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Fig. 2. (From Rieder's Atlas.)
Metamorphosis of the nucleus of the lymphocytes. (Combined picture from a preparation from acute leukæmia.)
To follow Fig. 1
In the normal blood of adults the number of the lymphocytes amounts to about 22-25% of the colourless elements.
Increase of the lymphocytes alone occurs, but in comparison with that of the other forms, much more seldom, and will be conveniently called by the special names of "lymphocytosis" or "lymphæmia."
2. Sharply to be distinguished from the lymphocytes is the second group: the "large mononuclear leucocytes." These are large cells about twice to three times the size of the erythrocytes. They possess a large oval nucleus, as a rule eccentrically situated and staining feebly, and a relatively abundant protoplasm. The latter is free from granulations, feebly basophil, and in contrast to the protoplasm of the lymphocytes stains less deeply than the nucleus. This group is present in normal blood in but small numbers (about 1%). They are separated from the lymphocytes because they are totally different in appearance, and because forms transitional between the two are not observed. It cannot yet be decided from which blood-producing organs these forms arise, whether from spleen or bone-marrow, although there are many reasons for regarding the latter as their place of origin.
These large mononuclear leucocytes change in the blood to the following kind:
3. "The transitional forms." These resemble the preceding, but are distinguished therefrom by deep notchings of the nucleus, which often give it an hour-glass shape, further by a somewhat greater affinity of the nucleus for stains, and by the presence of scanty neutrophil granulations in the protoplasm. The groups 2 and 3 comprise together about 2-4% of the white blood corpuscles[11].
4. The (so-called) "polynuclear leucocytes." These arise in small part, as will be described later in detail, from the above-mentioned No. 3, within the blood stream. By far the larger part is produced fully formed in the bone-marrow, and emigrate to the blood. These cells are rather smaller than Nos. 3 and 2 and are distinguished by the following peculiarities: firstly by a peculiar polymorphous form of nucleus which gives the relatively long, irregularly bulged and indented nuclear rod the appearance of an S, Y, E or Z. The complete decomposition of this nuclear rod into three to four small round single nuclei may occur during life, as a natural process. Ehrlich first discovered it in a case of hæmorrhagic small-pox; it is frequently found in fresh exudations. Formerly when various reagents, for instance acetic acid, were customarily used, the decomposition of the nucleus into several parts was more frequently observed, and Ehrlich for this reason chose the not wholly appropriate name "polynuclear" for this form of cell. As this name has now been universally adopted, and misunderstandings cannot be expected, it is undoubtedly better to keep to it. The expression "Cells with polymorphous nuclei" would be more accurate.
Fig. 3.
Nucleoli in larger lymphocytes.
(From a photograph of a preparation from chronic lymphatic leukæmia.)
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The nucleus stains very deeply with all dyes; the protoplasm possesses a strong attraction for most acid stains, and is unmistakeably characterised by the presence of a dense neutrophil granulation. The reaction of the protoplasm is alkaline, to a less degree however than in the lymphocytes. No free glycogen is contained in the polynuclear cells as a rule; nevertheless in certain diseases cells are always found which give a marked iodine reaction. In this manner the appearance of cells containing glycogen in diabetes was first proved. (Ehrlich, Gabritschewsky, Livierato.) The iodine reaction in the white blood corpuscles is also seen in severe contusions and fractures, in pneumonias, in rapidly progressing phlegmata from streptococcus and staphylococcus, after protracted narcosis (Goldberger and Weiss).
Ehrlich explains the appearance of glycogen as follows. The glycogen is not present in the cell as such, but in the form of a compound, which does not stain with iodine. This compound readily splits off glycogen, which then gives the iodine reaction[12].
We cannot regard the perinuclear green granules, described by Neusser in the polynuclear cells, as pre-existing. (See p. 42.)
The number of polynuclear leucocytes in the blood of the healthy adult amounts to about 70-72%, of the total white corpuscles. (Einhorn.)[13]
5. The eosinophil cells. These are characterised by a coarse, round granulation, staining deeply with acid dyes, and similar in other respects to the polynuclear neutrophils. With faint staining, a thin peripheral layer of the eosinophil granule is seen more deeply stained than the interior. The nucleus as a rule is not so deeply stained as in the polynuclear neutrophil, but otherwise in its general shape is completely similar. Both forms have in common a considerable contractility, which renders possible their emigration from the vessels, and their appearance in exudations and in pus. The size of the eosinophils frequently exceeds that of the neutrophils. Their number is normally about 2-4% of the white cells.
6. The mast cells. These are present, though very sparingly, in every normal blood; 0.5% is their maximum number in health.
Their intensely basophil granulation, of very irregular size and unequal distribution, must specially be mentioned. The granulation possesses the further peculiarity, in that with the majority of basic dyes it stains, not in the pure colour of the dye, but metachromatically—most deeply with thionin. As Dr Morgenroth found, the deviation from the colour of the dye is still more marked with Kresyl-violet-R (Mülheim manufactory), when the granules stain almost a pure brown.
The staining power of the nuclei is very small, and it is therefore hard to make out the shape of the nucleus without the use of difficult methods. In triacid preparations the granulation is unstained, and the mast cells appear as clear, polynuclear cells, free from granules.
So much for the colourless cells in the blood of the normal adult.
In pathological cases, not only do the forms so far mentioned occur in altered numbers, but abnormal cells also make their appearance. To these belong:
1. Mononuclear cells with neutrophil granulation. ("Myelocytes," Ehrlich.) Generally they are bulky, with a relatively large, faintly staining nucleus, often fairly centrally placed, and equally surrounded by protoplasm on all sides. A fundamental distinction from the large mononuclear cells lies in the fact that the protoplasm exhibits a more or less numerous neutrophil granulation. Besides the larger myelocytes, much smaller forms, approximating to the size of the erythrocytes are also found. All transitions between these two stages are likewise met with. In contradistinction to the polynuclear neutrophil elements, these mononuclear forms shew no amœboid movement on the warm stage. They form a constant characteristic of myelogenic leukæmia, and in these cases generally occur in large numbers.
Reinbach has found them in a case of lymphosarcoma with metastases in the bone-marrow. A. Lazarus observed their transitory occurrence in moderate number in a severe posthæmorrhagic anæmia. M. Beck observed them in the blood of a patient with severe mercury poisoning. They are also frequently found in children's diseases, especially in anæmia pseudoleukæmica infantum. K. Elze established their presence in a boy of 15 months, suffering from a slowly progressing tuberculosis of the lymphatic glands.
The appearance of myelocytes in infectious diseases is particularly interesting. Rieder had previously demonstrated that myelocytes may be present in acute inflammatory leucocytoses; and recently a thorough work by C. S. Engel has appeared upon the occurrence of myelocytes in diphtheria. Engel discovered the interesting fact, that myelocytes are often to be found in children suffering from diphtheria, and further made the important observation that a high percentage of myelocytes (3.6-16.4% of the white elements) only occurs in severe cases, and points to an unfavourable prognosis. Myelocytes are also present in mild cases, though not constantly and in much smaller number. Türk has recently undertaken a very exact and thorough analysis of their occurrence in infectious diseases, in the course of which he accurately tabulated the white corpuscles in a large number of cases. The results he obtained in pneumonia are especially characteristic, for he found at the commencement of the disease that myelocytes are not seen at all or only very scantily: and it is only at the time of the crisis, or directly afterwards, that they become specially numerous. In isolated cases the increase at this time was very considerable; and in one case amounted almost to 12% of all neutrophil cells.
2. Mononuclear eosinophil cells ("eosinophil myelocytes"). H. F. Müller was the first to point out their importance. They constitute the eosinophil analogue of the previous group, and are much larger than the polynuclear eosinophils; medium and small sized examples are often found in leukæmia. Eosinophil myelocytes are almost constantly present in myelogenous leukæmia and in anæmia pseudolymphatica infantum. Apart from these two diseases they are very rarely found; Mendel saw them for example in a case of myxœdema, Türk quite exceptionally in some infectious diseases.
3. Small neutrophil pseudolymphocytes. They are about as large as the small lymphocytes, possess a rounded deeply stained nucleus, and a small shell of protoplasm studded with a neutrophil granulation. The relatively deep stain of the nucleus and the small share of the protoplasm in the total cell body prevent confusion with the small forms of myelocytes, which never reach such small dimensions. The neutrophil pseudolymphocytes are exceedingly infrequent, and represent products of division of the polynuclear cells; they were first described by Ehrlich in a case of hemorrhagic small-pox. The process of division goes on in the blood in such a manner that the nuclear rod first divides into two to four single nuclei, and then the whole cell splits up into as many fragments. These cells occur also in fresh pleuritic exudations. After a time the nucleus of these cells becomes free, and the little masses of protoplasm thus cut off are taken up mostly by the spleen substance. The free nucleus likewise shares in the destruction. It is of the greatest importance that these cells, which up to the present have not elsewhere been described, should receive more attention. They must be of significance, in particular for the question of transitory hyperleucocytosis, which is by some referred to a destruction, by others to an altered localisation of the white blood corpuscles.
4. "Stimulation forms" were first described by Türk, and are mononuclear non-granulated cells. They possess a protoplasm staining with various degrees of intensity, but in any case giving with triacid solution an extraordinarily deep dark-brown, and further a round simple nucleus often eccentrically situated, stained a moderately deep bluish-green, with however a distinct chromatin network. The smallest forms stand between the lymphocytes and the large mononuclear leucocytes, but approach the first named as a whole in their size and general appearance. According to Türk's investigations, these cells often occur simultaneously with, and under the same conditions as the myelocytes. Their importance cannot at present be accurately gauged. Possibly they form an early stage of development of the nucleated red blood corpuscles, as the deeply staining and homogeneous protoplasm seems to indicate.
With the description of these abnormal forms of white corpuscles all occurring forms are by no means exhausted. We are here excepting completely the variations in size which particularly affect the polynuclear and eosinophil cells, and which lead to dwarf and giant forms of them. For however considerable the difference in size, these cells always possess characteristics sufficient for an exact diagnosis. But besides these, isolated cells of an especially large kind are found particularly in leukæmic blood, and concerning their importance and relationship we are up to the present in the dark.
FOOTNOTES:
[11] In enumerating the blood corpuscles, 2 and 3 may be counted separately or in one group.
[12] The assumption of Czerny, that the cells which react to iodine emigrate from suppurating foci, is without foundation. A simple investigation of freshly inflamed tissue is sufficient to show that the cells which have wandered from the blood stream soon contain glycogen.
[13] Kanthack described this group as "finely granular oxyphil" cells. Their granules stain red in eosine and in eosine-methylene blue solutions, but the colour is different from that of the true eosinophil cells, and much less intense. In the latter mixture they stain really with the methylene blue salt of eosine. Their true nature is shown by their behaviour with the triacid solution.