5 66 THE POPULAR SCIENCE MONTHLY. 



is an important matter in sustaining the intercranial flow. If the gen- 

 eral blood-pressure in the vessels of the head and neck is high and well 

 maintained, then a brain can work up to a much higher power, just as 

 a steam-engine may be worked up to a higher pressure, and so become 

 actually more powerful. 



While we recognize the fact that mental conditions are causally 

 associated with the amount of the blood-supply, indeed to a great ex- 

 tent rest upon it, it must not be supposed that I wish to under-esti- 

 mate the importance of the condition of the cerebi-al cells themselves, 

 either as to their inherited peculiarities, or as to the conditions pro- 

 duced by the experience of the individual. Such consideration is, 

 however, without the sphere of the present paper, which deals with 

 cerebral manifestations in relation to ordinary disease, and not with 

 those ailments which belong to the province of the alienist physician. 

 To one form of disorder of the cerebral cells alone may reference be 

 made here, and that is as to the effects of mental over-strain. Brain- 

 tissue can be developed by exercise, and worn out by overwork. 

 When this latter condition has been induced, there exists that irrita- 

 bility which forms part of the early stage of the exhaustion of nerve- 

 matter. In all overtried brains there is much irritability and ten- 

 dency to manifest what we term temper. This fact we learn in time 

 about the individual, but we are somewhat slow to recognize it in the 

 abstract. It is socially desirable and important that such recognition 

 be more general. 



In considering the associations existing between cerebral mani- 

 festations and certain conditions of the organism, and the effect exer- 

 cised by the latter upon the former, it is important to bear in mind 

 that the brain is divided into two vascular areas : 1. The anterior, 

 fed by the internal carotids ; and, 2. The posterior, fed by the basilar 

 artery ; nor is the amount of inosculation in the intercranial circula- 

 tion such as would allow vicarious action- to make good a deficiency 

 caused by an interference with the direct supply of either area. These 

 two vascular areas contain brain-cells with different properties and 

 functions. Tbei'e is much reason to believe that the emotions and 

 systematic sensations lie on the posterior area ; and that the intellect- 

 ual and motor powers, together with general peripheral sensations, lie 

 on the anterior area. In other words, the posterior area is associated 

 with the organic processes of the system ; the anterior with the ani- 

 mal life with the relation of the organism to its surroundings. The 

 vaso-motor nerves of these two areas are differently derived. The 

 nerves of the cerebral arteries spring from the lower ganglion of the 

 great sympathetic nerve in the neck, into which run the fibres ascend- 

 ing from the abdomen ; while the carotid arteries derive their vaso- 

 motor supply from the middle and upper ganglia. Thus we can see 

 how the emotions sympathize with the organic processes, especially 

 those located in the abdomen, and so can see melancholia in a new 



