538 PHYSIOLOGY CHAP. 



passive victims doomed to destruction. Other observations, 

 moreover, show that when the giant cells exhibit signs of necrosis, 

 they never contain leucocytes, as would be the case if Heidenhain's 

 interpretation were true. It is evident, therefore, that the 

 inegacaryocytes fulfil a phagocytic function within the body,, 

 which probably serves to free the lymphapoietic organs from the 

 leucocytes that are dead or in process of dissolution (van der 

 Stricht). 



P. Foa (1899) has recently investigated the experimental 

 conditions under which it is possible to obtain the phenomenon 

 of phagocytosis upon a large scale with these uiegacaryocytes. He 

 found it appeared vigorously in inanition, extensive burning of 

 the skin, and with intravenous injections of lecithin, milk, and 

 bacterial proteins, especially in gravid or very young rabbits 

 of VOD-SOO grams, in weight. Under all these conditions the 

 megacaryocytes were seen to contain numerous polymorphous 

 leucocytes within their protoplasm, some of which had already 

 undergone protoplasmic dissolution and nuclear fragmentation, on 

 the way to their complete disappearance. At the same time, the 

 protoplasm of the inegacjiryocytes was seen to undergo alteration 

 and disruption, and their nucleus shrank, and passed free into the 

 circulatory torrent, where it blocked the capillaries of the lungs 

 and was finally disintegrated. These two phenomena : destruction 

 of leucocytes by the megacaryocytes, and embolism of pulmonary 

 capillaries by the liberated nuclei of the giant cells, are always- 

 combined, and may be noted in a lesser degree under normal 

 conditions as well, particularly during pregnancy. In pathological 

 states the phenomenon is exaggerated, and indicates destruction of 

 leucocytes that are no longer capable of functioning.. 



Other notable facts show that the megacaryocytes exert an 

 important secretory function in regard to the regeneration of the 

 blood. In fact, after repeated bleeding of the rabbit, their number 

 conspicuously increases (van der Stricht, Bambeke, Heidenhain). 

 The external zone of their cytoplasm (which stains less readily) 

 exhibits bud-like protuberances, which increase in volume, and 

 become clearer in consequence of the increasing amount of fluid 

 imbibed by the delicate reticulum (Fig. 2'53). At a later stage 

 the said buds fuse one into the other, and form large clear vesicles, 

 in which it is no longer possible to distinguish the protoplasmic 

 network. When the intracellular tension of the secretory 

 product has reached its maximum, the fluid pours out, and the 

 distended protoplasmic reticulum contracts again to form a new 

 external stratum of cytoplasm. It should be noted that the bone 

 marrow of rabbits which have been freely bled seldom exhibits 

 leucocytes ingested by giant cells, showing that under these 

 conditions the secretory function of the latter predominates. 



We are ignorant of the precise physiological destination of the 



