PARTIAL ANAEMIA OF THE BRAIN. 21 1 



of abscesses, tumors, and other local diseases, induces symptoms of 

 Irritation or paralysis, according to the degree of the anaemia ; these 

 symptoms complicate those directly depending on the original disease, 

 and are due to functional disturbance of portions of the brain lying 

 beyond the actual disease. On autopsy, it is usually difficult or even 

 entirely impossible to decide, whether oedema and capillary anaemia 

 exist in the vicinity of an abscess, tumor, etc., and how far they ex- 

 tend. But we have a right to suppose that the vicinity of these points 

 of disease is in a similar state to that of parts affected in the same 

 way, which are exposed to observation ; and we are the more justified 

 in this supposition, because for a long time it has not escaped the more 

 accurate observers that, in many cases of partial disease of the brain, 

 symptoms occur that cannot depend on the coarser structural changes 

 of the brain found on autopsy, but must be referred to an impercep- 

 tible participation of other portions of the brain lying in the vicinity 

 of the affected part. It is most probable that this participation 

 depends on disturbance of the capillary circulation and the occurrence 

 of oedema, because in other parts of the body also these anomalies 

 often leave no traces. Occasionally the symptoms observed during 

 life give a better means of judging of the extent of the secondary dis- 

 turbances of circulation, or of the collateral oedema, than the autopsy 

 does. For instance, if paralysis and spasm accompany a disease of the 

 cortical and medullary substance of the cerebrum, which does not 

 encroach on the cranial cavity, and whose destruction does not induce 

 paralysis and spasm, there is probably an anaemia extending to por- 

 tions of the brain lying far deeper. As numerous examples have 

 proved that an entire half of the cerebellum may be destroyed without 

 inducing hemiplegia, we cannot refer a hemiplegia, observed along 

 with structural changes confined to the cerebellum, directly to that 

 organ, but must consider it due to the extension of collateral oedema 

 to portions of the brain whose loss of function causes paralysis of half 

 the body. The strange experience, that, in disease of one side of the 

 cerebellum, there is sometimes no hemiplegia, at others there is hemi- 

 plegia of the same side, and in still other oases that it occurs on the 

 opposite side, is doubtless due to the fact that, in the latter cases, a 

 collateral oedema extends along the crura cerebelli ad frontem to the 

 lateral regions of the pons ; while, in those cases where the same side 

 is affected, the oedema extends along the crura cerebelli ad medullam 

 oblongatam to the lateral branches of the medulla oblongata; and 

 where there is no hemiplegia the collateral oedema has not advanced 

 .n either direction to regions whose loss of function involves that symp- 

 tom. These examples may suffice to show how important a r61e par- 

 tial anaemia of the brain, due to collateral oedema, plays in the symp- 



