DIFFERENT RACES OF MANKIND. 347 



of the brain, in cubic inches." It is superfluous to point out that the brain, or the 

 mass of cerebral matter designated by anatomists the encephalon, Avhich embraces the 

 cerebrum, the cerebellum, the j^ons varolii and the medulla oblongata, and which is 

 contained in the cranial cavity, does not absolutely fill that cavity. This is far from 

 being the case. There are also the membranes which cover these organs, one of 

 them, the dura mater, being thick and tolerably bulky ; the blood contained in the 

 vessels of these membranes ; and, especially, the serous fluid which is in connection 

 with the membranes and in the ventricles. It is obvious that the volume or the 

 weight of the two former must vary considerably, and in the case of the latter great 

 diversity of amount prevails. The serosity must be regarded as a necessary com- 

 pensatory fluid which fills up the cavity of the cranium perfectly, however much the 

 cerebral mass may change in size. In the early periods of life the brain is rich in 

 serosity ; as maturity is approached it becomes more firm and dense, and is freest 

 from serous fluid. But as soon as this meridian period of life is passed, and decline 

 commences, the watery fluid in and about the brain again increases, and goes on 

 doing so until extreme old age. Besides these normal changes in the amount of 

 serous and other fluids contained in the cavity of the skull, this" amount will also 

 vary according to the disease which terminates life, whether it be an acute or chronic 

 disease. Hence it will be at once apparent that the serosity itself is so variable as 

 not easily to be reduced to any rule, and that no rule for its estimation can be estab- 

 lished which can be absolutely applicable, or apply to each individual case. To meet 

 these difiiculties it has been proposed, as the best practical expedient, to make a de- 

 duction, allowance, or tare, for membranes and fluids, which shall bear a definite 

 proportion to the size of the cranial cavity, — be larger where this is capacious, and 

 gradually diminish as it decreases, so as to become decidedly less when this cavity 

 and the organs contained in it are small. For this purpose an average percentage 

 allowance has been fixed upon. At first fifteen per cent, was regarded as the proper 

 allowance to be made, but further investigation has led me to fix upon seventeen per 

 cent, as the most generally applicable ride where the mode of gauging to be immedi- 

 ately mentioned is followed, and approaching most closely to the result of actual 

 metrological experiments. In the tables of the weights of the brains, calculated from 

 internal capacities of skulls, which are to follow, an allowance or tare of seventeen 

 per cent, has always been deducted, as a compensation for the membranes and fluids. 

 By this means, if we do not strictly regain the absolute weight of brain of the indi- 

 vidual in each case, we shall approach so nearly to it on an average that for all 

 practical purposes the results may be regarded as correct, — undoubtedly much more 

 so than any that have preceded them upon any comprehensive scale. 



By the great politeness of a most industrious and able working anatomist and 

 craniolo"-ist in Austria, Dr. A. Weisbach, I have been favored with the results of his 



