Histology of the Blood, Normal and Pathological

by Paul Ehrlich; Adolf Lazarus

Whilst for instance the majority of the granules are more or less rounded forms, in some classes of animals, e.g. in birds, the analogues of the granules of mammalian blood are characterised by a decided crystalline form, and a strong oxyphilia. The substance of the mast cell granulations is also crystalline in some species of animals.

The size of the individual granules is constant in any animal species for every kind of granule—excepting only the mast cells. The eosinophil granulation reaches its greatest size in the horse, where really gigantic examples are found.

The presence of granulated colourless blood-cells has been demonstrated in the most various classes of animals, and even in the blood of many invertebrates, particularly, as Knoll has shewn, in the Lamellibranchiates, Polychætes, Pedates, Tunicates and Cephalopods. Concerning vertebrates, especially the higher classes, accurate and ample researches are to hand. In birds we recognise two oxyphil granulations, of which one is embedded in the cells in the crystalline, the other in the usual granular form. Amongst the vertebrates most investigated classes possess granulated polynuclear cells. To this circumstance Hirschfeld has recently devoted a thorough paper containing many details worthy of note. In the majority of the animals observed, he found too that the polynuclear cells contained neutrophil granules; in only one animal, the white mouse, did he find them, or granulations analogous to them, completely wanting.

According to the investigations carried out some years back in Ehrlich's laboratory by Dr Franz Müller, these results of Hirschfeld's must be described as inaccurate. After many vain endeavours, Dr Müller was able to find a method by which numerous though very minute granules could be found in the polynuclear cells of the mouse. The case shews that it is not permissible to assume the absence of granules, when the ordinary staining methods are not at once successful. There is no universal method for the staining of granules, any more than for the staining of various kinds of bacteria. Indeed all granules, that are easily soluble, vanish when the triacid method is used, and so a homogeneous cell protoplasm is simulated.

But naturally, the occurrence of non-granulated polynuclear cells in certain classes of animals is not to be denied from these considerations. Hirschfeld asserts that such cells occur side by side with granulated cells, for instance in the dog; and draws from them far-reaching conclusions as to the meaning of the granules. From Kurloff's work (see p. 85) we must insist, on the contrary, that there is no evidence that the non-granulated polynuclears are identical with the granulated cells. Kurloff has shewn, at least for guinea-pig's blood, that these two heterogeneous elements are to be sharply separated one from the other, and that they have an entirely different origin.

Specially important for a theory of the nature of the granules is the circumstance, that generally speaking in all species of animals they are present in those cells of the blood only which are adapted to and capable of emigration. That a certain nutritive function is to be ascribed to the emigration of the granulated cells is a very obvious supposition, scarcely to be denied; and naturally cells with a plentiful store of reserve material are eminently suited for this purpose. The lymphocytes on the contrary, incapable of emigration, are almost totally devoid of specific granulations.

A further indication that the granulations really are connected with a specific cell activity lies in the fact, that one cell bears but one specific granulation. The contrary assertions that neutrophil and eosinophil, or eosinophil and mast cell granulations occur in the same cell Ehrlich regards as unfounded, from extensive researches specially directed to this point. Nor has Ehrlich seen a pseudoeosinophil cell of the rabbit change to a true eosinophil[23]. That such a transition does not occur is most distinctly shewn by the fact that the various granulations behave entirely differently towards solvents. With the aid of acids, for example, the pseudoeosinophil granules can be completely extracted from the cells, whilst the eosinophil granules remain whole under this process, and can now be stained by themselves.

The clearest proof that the neutrophil, eosinophil, and mast cells are entirely separated from one another by the fundamental diversity of their protoplasm, of which the granulation is but a specially striking expression, is afforded by the study of the various forms of leucocytosis. As will be shewn in detail in the following chapter, neutrophil and eosinophil leucocytes behave quite differently in their susceptibility to chemiotactic stimulation. Substances strongly positively or negatively chemiotactic for one cell group are as a rule indifferent for the other; frequently indeed there is an exactly opposed relationship, inasmuch as substances which attract the one kind repel the other. Still greater is the difference between the mast cells and the other two cell groups; for so far as present investigations go, they are quite uninfluenced by substances chemiotactic for the neutrophil or eosinophil cells.

As specific cellular secretions, various kinds of granules must also be sharply marked off from each other by their chemical properties. The granules of the blood corpuscles seem to be of very simple chemical constitution. We have special grounds for the assumption that the crystalline granulations are for the most part composed of a single chemical compound, not necessarily highly complex even, but which seems to be a relatively simple body such as guanin, fat, melanin, etc. Doubtless other granulations have a more complicated constitution, and very often are a mixture of various chemical substances. The most complicated granules of the blood are the eosinophil, which are, as has elsewhere already been mentioned, of a more complex histological structure. For a peripheral layer is plainly distinguishable from the central part of the granule. It should be mentioned that according to Barker the eosinophil granulations appear to contain iron.

The key-stone of the hypothesis of the secretory nature of the granules is the direct observation of a secretory process in the cells bearing the granules. Naturally these researches offer extraordinary difficulties since only the coincidence of a number of lucky circumstances would allow the passage of dissolved granule substance into the neighbourhood to be followed. Kanthack and Hardy have succeeded in demonstrating the secretory nature of the eosinophil granules of the frog. When, for example, anthrax bacilli are introduced into the dorsal lymph sac of the frog they exert a positive chemiotaxis on the eosinophil cells. The latter come in contact with the bacilli, and remain for some time attached to them. During this period Kanthack and Hardy observed a discharge of granules from these cells, which now possess a protoplasm relatively homogeneous. Afterwards these cells move away from the bacilli, and are succeeded by the polynuclear neutrophil cells, as will be mentioned later. These authors were further able to observe gradual accumulation of granules in eosinophil cells in lymph kept under microscopic observation as a hanging drop, and thus demonstrated that they undergo the two stages characteristic of secretion, (1) appearance of granules within the cells, (2) discharge of these granules externally.