THE CIRCULATION OF THE BONE-MARROW. 41 



sinusoidal capillaries are discrete and are perhaps never, or almost never, in the 

 direct line of the circulation. Furthermore, the organ is inclosed within rigid bony 

 confines, frequently with bony trabecular subdividing the marrow-substance, a con- 

 dition as far as possible from that found in the contractile spleen. The spleen and 

 the bone-marrow are unlike both structurally and physiologically, and without 

 any real basis for analogical comparison. C. K. Drinker, in association with K. R. 

 Drinker and C. C. Lund, to whose work reference has already been made, 

 attempts to explain the circulation of the bone-marrow in relation to its physio- 

 logical function. He has found that no experimentally induced increase of pressure 

 will cause an increased discharge of cellular elements from the marrow into the general 

 circulation. He has been unable by any physiological method to "wash out" the 

 developing cells of the marrow. The red cells are delivered into the circulation in 

 cycles at varying intervals, independent of circulatory influences. The areas 

 of developing red cells, as seen in the bone-marrow, show all the cells in a given 

 area to be in the same phase. Drinker hypothesizes a "growth pressure" delivery 

 of these blood elements into the general circulation after first having "grown 

 through" the extremely delicate walls of the sinusoids. This process occurs peri- 

 odically and without any definitely demonstrable relation to the blood-pressure 

 or circulation and obviously without the possibility of any inherent expansile- 

 contractile mechanism. 



In injections of the white rat, the marrow (of the ribs particularly) showed 

 the same gross vascular arrangement as that described for the long bones of the 

 pigeon. There were two central vessels with transverse branchings giving rise to 

 an extensive plexus toward the circumference. In a few experiments on the rabbit, 

 cat, and dog, the normal marrow of both the radius and ulna showed the same 

 general characteristics, though in an apparently less extensive degree throughout 

 the shaft. An occasional section from the mammalian tissues presented here and 

 there the typical inter-sinusoidal, semi-collapsed type of channel, with a few fine ink 

 granules marking its existence. Drinker and his coworkers find these same indi- 

 cations in their most carefully controlled mammalian injections. One of their 

 figures shows a single inter-sinusoidal lumen, as identified by a perceptible line 

 of fine ink granules, identical in appearance with the channels we have seen so 

 much more extensively distributed in the pigeon. While the primary purpose for 

 inducing a hypoplasia of the pigeon's marrow was that more accurate cytological 

 relationships might be determined, it may be, as Dr. Drinker has suggested, that the 

 hypoplastic marrow, through an increased fluidity supplanting the depleted cellular 

 areas, has provided the optimum conditions for demonstration by injection of 

 this otherwise non-demonstrably patent or occult system. In other words, the 

 normal incompressibility of the marrow-tissue within its bony cavity may be 

 altered. If such be the case, a similar condition of induced hypoplasia in the mam- 

 mal must precede the demonstration of the completeness of the analogy between 

 the vascularization of avian and that of mammalian marrow. This is a problem 

 in itself, inasmuch as simple starvation of the mammal will not produce the 

 hypoplasia desired. 



