THE EPIDEMIOLOGY OF ENTERIC FEVER AND CHOLERA IN HAMBURG
1105 be noted, however, that the blood pressure was probably very low at this stage of the experiment. We have seen that dilatation of the pupil is still obtained after section of the sympathetic. No vaso-motor fibres are known to run to the iris except by way of the sympathetic, and even if such exist the experiments of Langley and Anderson tend to show that vascular effects are inefficient to bring about the dilatation observed. Moreover, it is well known that changes in blood pressure may
... ood pressure may occur from stimulation of various parts of the cortex, whereas pupil dilatation only occurs from certain localised spots in the absence of the epileptoid state. It seems justifiable from these considerations to regard the effect as another example of direct inhibition of the oculo-motor nerves from the cortex. There is no lack of evidence as to the presence of fibres connecting the cortex with the mesencephalon and some of these must be regarded as the ones concerned in the pupillary effects. We may leave -out of the question the dilatation of the pupil which accompanies the epileptoid state, for this is undoubtedly of an extremely complex nature, requiring special investigation. Confining our attention to the more specialised results obtained from the oculomotor area in the posterior part of the frontal convolutions which are to be looked upon as part of the fronto-parietal motor or kinaesthetic area and quite distinct from the more anterior or so-called prefrontal area, and to the results obtained from the oculo-sensory or visual area in the occipital convolutions we find definite anatomical connexions with the lower centres. The pallio-tectal or cortico-mesencephalic system of fibres has recently been thoroughly investigated by Dr. C. E. Beevor and Sir Victor Horsley. It is noteworthy that no fibres were found passing to the mesencephalon from the frontal region—i.e., from the area of cortex in front of the excitable cortex. From lesions of this part there was marked degeneration of the fronto-thalamic fibres previously described by Dejerine ; the only mesencephalic centre to which fibres could be traced was the upper or anterior part of the locus niger. No fibres, therefore, go to the tectum. A large number of fibres could be traced from the excitable cortex to the corpora quadrigemina and mesencephalon, especially to the superior colliculus. This was very marked in the cat, much less so in the monkey. The fibres from the oculomotor areas have not yet been specially investigated. The results from lesions of the occipital lobes were particularly striking and confirmed Edinger's researches on birds. In proportion as more of the area of the cortex containing 'Gennari's streak is involved in the lesion the number of degenerated fibres passing to the colliculus increases. The fibres are large and stand out distinctly from the mediumsized occipito-thalamic and occipito-geniculate fibres and from the small callosal fibres and fine collaterals which enter the corona radiata in large numbers. Some of the occipito-tectal fibres pass among the fibres of Gratiolet's radiation, others run through the mesial region of the inferior longitudinal bundle. All the fibres are distributed to the whole breadth of the stratum griseum profundum of the superior colliculus. Which of these fibres are concerned in the pupillary phenomena, and whether they pass, any of them, directly to the superior pupillo-dilator centre or to the pupillo-constrictor centre, or only by intermediate connexions, must be left for future research to determine. I have already shown that the cortical pupillo-dilatatin is a complex event, strikingly resembling the ordinary sensory dilator reflex in that it is accompanied by all the usual effects of stimulation of the cervical sympathetic as long as that path is intact, but that it also occurs, deprived of the other sympathetic effects, when this nerve is divided. The evidence is therefore in favour of a more circuitous course, or at any rate of multiple and complicated interconnexions. There is evidence that pupillo-constriction can also be elicited from stimulation of the cortex. Ferrier obtained it from stimulation of the anterior and posterior limbs of the angular gyrus in the monkey, but this observation is prob ably incorrect. I have already stated that I failed to confirm the same observer's result from the third external or coronal convolution in dogs. In pigeons Ferrier found intense constriction of the pupil from excitation of the middle of the convexity of the hemisphere. Sobafer obtained marked constriction of the pupil from stimulation of the quadrate lobule in monkeys. This brings us to the consideration of the exact nature of the phenomena. The ,view of Bechterew and Mislawski that we have here the central prolongations of the cervical sympathetic is, apriori, highly improbable, or, at any rate, a misleading explanation of the results ; indeed, the continuance of the dilatation after section of the cervical sympathetic proves that it can only be partially true. So, too, it is unlikely that we are dealing with "centres" for the pupils in the ordinary sense of the term. We have found that the effect is most specifically obtained from the areas which are most concerned with ocular movements whether from the motor or the sensory side ; moreover, it would seem that the effect is indissolubly connected with those movements and does not occur in their absence, hence it is most reasonable to conclude that the phenomenon is an associated effect. As regards the so called sensory areas-i.e., the visual centres in the occipital cortex-it is probable that the attention plays some part. We produce, by artificial excitation, some strong but probably ill-defined visual sensation which arouses the attention and leads to the appropriate movement of the head and eyes towards the direction from which the stimulus seems to proceed. The sensation is strong and sudden and is accompanied by dilatation of the pupils in no physiological sense other than the expression of emotion. IN order to understand aright the epidemiology of enteric fever and cholera in Hamburg it is necessary to have a clear picture in one's mind not only of the topography of the town but also of the topographical arrangement of the surrounding district, for the reason that the particular conditions of our locality are in a special manner favourable to the diffusion of enteric fever and cholera from the town to the country and from the country to the town. Hamburg, as you are aware, is situated in the great North German lowland, which is of diluvial origin, made up of glacial drift, sand, clay, gravel, and erratic boulders, scattered pell-mell, overlying the tertiary formation, and in many places rising like a plateau to a height of 50 metres and more above the level of the sea. This formation, which is, comparatively speaking, poor in water, is termed by us the " geest." " At the sea-coast and mouths of rivers lies the alluvial formation, the marsh," which extends in front of and beyond the geest." It is, however, only met with in those parts where there are an ebb and flow-that is to say, only at the North Sea, not at the Baltic. These marshes consist of the sediment deposited by large rivers which empty themselves sluggishly into the sea by wide mouths. It is only through the activity of man in building °' dikes" or embankments that they are made habitable and secure against floods. In some places they form islands between numerous water-courses ; in others they form a wide boundary to the " geest," covering miles of flat expanse at sea bays and mouths of the river. Hence it is clear that the part of the estuary of the Elbe, as far as above Hamburg, once formed a deeply indented bay ( Fig. 1 gives a picture of these conditions). The marshes are very damp and are intersected by numerous drains which at low tide empty themselves into the river by means of sluices. A somewhat larger drain which flows parallel with the embankment goes by the name of the " Wetternng." " The dwellinghouses lie on the inside of the embankment, between it and the "Wetterung," at irregular intervals, in even rows, extending for miles. The fertile land lying behind is used for feeding cattle and growing vegetables. As naturally follows from such an arrangement of the houses, every kind of refuse from the dwellings, cattlestables, and dunghills very easily finds its way into the "Wetterung," which at the same time is used for drinking and domestic purposes. For all water from the marsh wells contains so much iron that it cannot be used for drinking purposes. And in cases where the "Wetterung" is not 1 A paper read before the Epidemiological Society on March 18th, 1904.