A close analogy can also be drawn with cases of embolism. The writer has shown that embolism involving only parts above the basal ganglia does not cause coma. Inasmuch as in many of these cases a large patch of brain-tissue is involved, and as, further, the sudden ness of the attack must be equal, what ever the part involved, it follows that here again much must depend on the particular structures included, for smaller infarctions, if only they involve the ganglia, often do bring on coma.
It can consequently be stated that, whatever accessory influences there may be, there are but two important govern ing factors in the development of coma: the size of the hremorrhage and the particular part of the brain implicated. These deserve a little further considera tion.
_Lis to the amount of hmmorrhage that will of itself cause coma, experiments on animals by Pagenstecher, von Schulten, and others have led to the conclusion that in the human being one and a half to two ounces is about the extent of limitation of the brain-space that can be borne without interruption of psy chical functions. (Afore can be tolerated in a diffuse effusion like a meningeal hmmorrhage than in a confined focus.) The exact amount thrown out in a case of apoplexy is rarely, if ever, known, since some of the fluid is promptly ab sorbed or scattered, and, independent of that, it is impossible to more than esti mate the volume of these irregular foci. So far as such rough estimation goes, it corresponds fairly with the experimental results. This applies to cases in the hemispheres (pallium). When the size of an effusion is stated to be that of a hen's egg, it may be considered to equal two ounces of fluid. Hence, hremor rhage of that bulk should be, and in practice is found to be, on the border line. It may be expected to at least produce stupor and frequently some coma. When of greater volume, coma very generally results. In the basal ganglia, however, a much smaller amount may suffice.
The principle here is that the effusion, by its volume,exerts such a general press ure on the whole cortex as to obtund consciousness. Of the sufficiency of this factor there is no question. It may act by producing an anmmia or by more direct mechanical effect. Further, a compression, before ineffective, may be come sufficient if the arterial pressure sinks.
As to the susceptibility of different parts, injury below the oblongata (i.e., in the cord) does not cause coma. The
syncope of shock or even sudden death may result, but not real coma. And it is uncertain whether hmorrhage of the oblongata has much tendency to pro duce coma; most such cases are small and any stupor is masked by respiratory and other phenomena. In the old case of Fabre (quoted by Gintrac and others) sonic loss of conseionsness attended a small luemorrhag.e of the left pyramidal body. But in several other cases of small effusion in other parts of the oblongata no distinctly comatose condition has de veloped.
t\.t the other brain-pole—i.e., corticad of the central ganglia—lye have already seen that coma is essentially a conse quence of general brain-compression. In this major portion of the encephalon there is little difference between the vari ous parts. Apparently the occipital lobe tolerates infringement better than the frontal and parietal lobes; but there is no decisive difference.
Regarding the cerebellum, the general opinion agrees with the evidence that uncomplicated hTmorrhage when mod erate in amount does not invoke coma. But in these rather rare cases either rupture occurs or, if much size is at tained, there is so much pressure on sub jacent structures as to obscure the bear ing of the case.
There still remains the region of the central ganglia, the cerebral crura, and the pons. Ihemorrhage of the caudate nucleus is prone to bring on coma. That in the lenticular nuclei and in the thal ami is somewhat less apt to do so. 'When in a cerebral crus, there is commonly some coma or, at least, stupor, though these hfemorrhages are rarely volumi nous. Those of the pons are most in clined to cause coma, though usually small unless they have already ruptured. A comparison of this last group of cases (involving the brain-stem) brings out forcibly one fact already referred to,— viz.: that hmmorrhages in the sensory path show but little tendency to cause coma, while those in the motor path have a marked tendency in that direc tion. This fact stands out quite as clearly when they are compared by vol ume. It is, of course, not certain whether this applies specially to the mo tor tract or to other and less under stood tracts closely associated with them; it may be fibres to the so-called somms thetic area. So far as this coma-zone has been noticed in the past, it has been thought to depend upon the fact that here were grouped fibres passing to, and thus influencing all parts of, the brain.