With regard to the significance of the blood platelets, most authors, of whom we should before all mention Hayem, Bizzozero, Laker, assume justifiably that they are preformed in the living blood. The view opposed to this, advocated more particularly by Löwit, that these forms first arise in the blood after it has left the vessels, we may describe on the grounds of our own extensive observations as inaccurate.
The blood platelets, on the grounds of their small size and complete lack of nuclear substance, are generally regarded as not analogous to real cells. Whether they represent intravital precipitation of substances of the plasma, or whether they are budded off from the cells, cannot at the present be decided with certainty, though many facts seem to support the latter assumption. That they contain glycogen (see p. 45), marks them as descendants of the blood cells. Moreover, appearances are often met with in dry preparations that arouse the suspicion that the platelets arise from the red blood corpuscles (Kœppe). Arnold has further observed processes of budding in the red blood corpuscles not only extravascularly but also intravascularly in the mesentery of young guinea-pigs, and has seen the elements that were cut off change into forms free from hæmoglobin.
Our knowledge too of the physiological function of the blood platelets still needs much amplification. The original view of Hayem, who regards the blood platelets as early stages of the red blood discs, and for this reason calls them "hæmatoblasts," is, according to the judgment of most hæmatologists, untenable.
Nearly all more recent papers, on the other hand (cp. Löwit's compilation), recognise the close connection of the blood platelets with coagulation, first observed by Bizzozero. Whether the substance of the platelets directly yields the material for fibrin formation, as Bizzozero holds, or whether according to the observations on thrombus production of Eberth and Schimmelbusch they play but a subordinate part, is not yet decided. To enter here into the chemical side of this complicated problem, would lead us much too far, and we will only refer to a few clinical observations which illustrate the relations between the clotting power of the blood and the number of platelets it contains.
Marked increase of the blood platelets occurs in chlorosis (Muir) and in posthæmorrhagic anæmia (Hayem). In both conditions there is a decided increase in the clotting power of the blood. In contrast, is the important observation of Denys, who found in two cases of purpura, where as is well-known the clotting power of the blood is always much lowered or may even be entirely destroyed, only one morphological blood change, a very marked diminution of the blood platelets. Ehrlich likewise had occasion to examine a similar case, in which the blood platelets were entirely absent.
H. F. Müller has described a fourth formed constituent of the blood, and given it the name of "hæmoconiæ" or "blood atoms," "blood dust." It is found in the plasma of the blood as very small granule- or coccæ-like colourless corpuscles, highly refractile, with a very active molecular movement, which keep their shape under observation for a very long time without any special precautions. According to Müller these bodies are not blackened by osmic acid, and probably contain no fat; they seem to have no connection with fibrin formation, as they always lie outside the fibrin network. Müller found them in every normal blood, in varying numbers however; much increased in a case of Morbus Addisonii; diminished in hunger and cachexias.
More detailed observations are necessary to determine the chemical nature of these forms. Experiments in this direction by extraction with ether, or by the use of fat staining substances, alkanna, Soudan dye, and comparative investigations on lipæmic blood should be successful.
FOOTNOTES:
[36] The physiological figures found by Brodie and Russell with the aid of this method exceed considerably those of earlier authors. They found a proportion of platelets to erythrocytes of 1:85 or an absolute number of about 635,000 per mm.{^3}