THERMOMETRICAL OBSERVATIONS TAKEN AT THE MILITARY HOSPITAL,

ST MARY'S, BATHURST, FOR THE MONTH OF AUGUST 1866.

Wet.

Dry.

Maximum and Minimum Thermometers.

DAYS.

THERMOMETRICAL OBSERVATIONS TAKEN AT THE MILITARY HOSPITAL, ST MARY'S, BATHURST, FOR THE MONTH OF SEPTEMBER 1866.

CHAPTER III.

1. THE EFFECTS OF TROPICAL HEAT ON THE GREAT NERVOUS CENTRES, AND ON THE VITAL PROCESSES OF THE INHABITANTS OF TROPICAL CLIMATES.-2. THE INTERIOR TEMPERATURE OF THE GLOBE.

THE effects of great tropical heat on the intellectual faculties of man is indeed very marked, especially when continuous; it seems, in the first place, to interfere with the regular nutrition of the cerebrum, producing a modification in the associative connections of ideational consciousness, and consequently interferes in some degree with the transmission of external expression made on that organ to the sensorium-the centre of consciousness.

One great example may be adduced from the want of success with which, in tropical climates, individuals in many cases attempt to exert the will to the recall of events which had previously been before their consciousness, but which do not at the time automatically or spontaneously present themselves in it. We very often hear the complaint, that "The heat has destroyed my memory. I cannot recollect anything." The individual fixes his attention upon ideas which had already been present in his consciousness, and places the full weight of his mind to it so as to intensify these ideas, and thus suggest and strengthen those associations which were connected with the circumstances under consideration, and yet he hesitates and bungles, and cannot give a positive and direct statement as to the facts.

nutrition of

Effects.

The effect of this modified nutrition, occasioned by the con- Modified stant exposure to heat, is to produce a species of absent state the brainof the mind, a weakness of the "bond of direct association," whereby the thoughts do not so quickly develope themselves when we attempt to recall events which at some past period had produced impressions of sensational consciousness, as when the events appeal directly to our ideational consciousness.

tervals.

But this state of absent consciousness is not permanent, Lucid insince there are lucid intervals when the mind appears to be in perfect activity, and when the process of aggregating and collocating ideas, of decomposing complex ideas into simple ones, and of combining simple ideas into general expressions, is performed to a great extent automatically; and thus many philosophers believe that the same amount of mental and bodily application which is shown in temperate climates can be performed in the tropics-that the same vivid train of thought, the same mental consciousness and reasoning faculties, can be there exercised-in a word, they believe that there exists the same central activity, which, when our attention is fixed upon a certain class of ideas, suggests to our consciousness the same train of thought, in continuous and rapid succession, independently of our will, or without any purposed direction of our will to it, as is met with every day in temperate climates. This condition, when duly considered and examined, it will be admitted, forms an a priori argument, which cannot possibly be attained in tropical climates.

heat on the

tropics.

The foregoing statement exhibits, without a doubt, the reasons Effects of why natives of tropical climates do not show the same active native of the development of the intellectual faculties, especially of the reasoning processes, as natives of a temperate climate. Thus, with the former, the combination of suggestive ideas so as to produce important results in a material form, can only with great difficulty be obtained; and since this alone is the great source of improvement in knowledge, it is no wonder that the natives of tropical climates are deficient in the fundamental principle of education, whilst, on the other hand, those of

Mental fatigue from heat.

Results of high tem

perature on Jollofs.

temperate climates have every facility offered them. The young native inhabitants of the tropics do not undergo any proper mental cultivation; the fixation of their attention to certain objects, exclusively of many others, is not made the constant study of their parents, who do not instruct them to call into their understanding the relation and connection which exists between different ideas, nor how to isolate ideas and recognise their common properties. They do not withdraw their minds from those noxious influences which may occupy their mental activity-from what is sensual and debasingand thus bring in appropriate ideas or fertile and productive faculties which will direct and invigorate, cultivate, and chasten their youthful consciousness.

Again, in tropical climates, the uninterrupted application of the intellectual or reasoning faculties for a few hours on any particular subject produces great mental fatigue; the automatic or attractive power, after a very short time, becomes incapable, or finds it difficult, to rivet the attention on the class of ideas under consideration; and the thoughts, in consequence, either wander from the subject or do not "develope themselves consecutively in the mind;" and very often the individual complains of severe headache or vertigo. In temperate climates the case is very different; the author, whilst at college in England, requently occupied fourteen out of the twenty-four hours in hard study without any evil result, but since his return to the tropics he finds six hours to be his utmost limit of continuous application without producing severe mental fatigue; and even this period he finds to diminish the longer he remains in the tropics. In the northern portions of Western intertropical Africa, viz., Senegal and the Gambia, the temperature, as has been demonstrated in the preceding chapter, is at certain seasons extreme, being continuous for several days from 102° to 110°; and the effects of this heat, per se, independently of any local. condition, have decidedly ulterior influences in the reproduction and development of the inhabitants occupying these regions. The heat has of itself a great influence in increasing