562 THE POSTERIOR PITUITARY AND THE NERVOUS SYSTEM. 



says Morel. How true this is is emphasized by the precaution 

 Nature takes to nourish the nerve throughout its entire length 

 and thus to insure the conversion of the chemical energy con- 

 tained in its myelin and the plasma into nervous energy. 



THE MINUTE CIRCULATION OF THE CEEEBRO-SPINAL SUB- 

 STANCE. Such a circulation as that suggested by this title is 

 not thought to exist. Both in the central ganglionic and in 

 the cortical arterial systems the arteries are now believed to 

 be "terminal": i.e., to neither supply nor receive any anas- 

 tomotic branch. They penetrate the cerebral substance to 

 terminate there. The veins are similarly disposed. Deprived 

 of valves and muscular tissue, they are likewise considered as 

 "terminal" in the sense attributed to that word in respect to 

 the arteries: a normal outcome of the absence of connection 

 with the latter as supposedly indicated by the impediment 

 presented to the injection of fluids in them. And yet, how 

 does the blood, with its corpuscles, find its way from the ar- 

 teries to the veins? Does it filtrate through the arterial walls, 

 find its way through the lymph-spaces to the venous walls, 

 and reach the sinuses? Of course, we have elsewhere in the 

 organism both the effusion of plasma and the emigration 

 of corpuscles through vascular walls; but this is a process of 

 a different kind, and for which the blood-stream only plays 

 the part of purveyor; it represents the main factor of a repara- 

 tive and protective function, of which, indeed, the cerebro- 

 spinal system is a prominent beneficiary when need be. There 

 is a wide margin, however, between this process and the mech- 

 anism of circulation, which includes channels beginning at the 

 heart and ending in this organ, and having for its purpose, not 

 only to carry oxygen to all parts of the organism, but also to 

 rapidly remove blood as fast as its oxygen-ratio is being re- 

 duced. "Terminal" vessels do not satisfy this sine qua non 

 of perfect metabolism in the cerebro-spinal system, notwith- 

 standing the presence in the superficial structures of more or 

 less close capillary net-works. Indeed, the very presence of 

 these capillaries seems to us to point to these deeper "ter- 

 minals" as incongruities. 



The marked evidences of engorgement so typically shown 

 by Berkley's illustrations, and to which we have referred, are 



