April 3, 1885.] 



♦ KNOWLEDGE ♦ 



275 



on the spot. The head is hotter than the trunk -when the 

 muscles are reposing and the brain working hard, and so 

 ■with otlier organs. 



Oxygen enters the blood at the lungs, and carbonic acid 

 leaves it there ; but this docs not prove that the ]iarticiilar 

 carbonic acid that is expired at oue moment is due to a 

 combination of carbon -with the particular oxygen df the 

 immediately previous inspiration. It is far move probable — 

 or I may say it is certain — that the dark venous blood is a 

 carrier of the oxidised carbon produced by tho general com- 

 bustion taking place throughout the body, and that it gives 

 out some of this as carbonic acid on reaching the lungs, 

 and that it takes in some oxygen, becoming thereby arterial 

 blood, the which red arterial blood carries round tho oxygen 

 to support the general bodily combustion. 



The carbonic acid and the oxygen may be thus carried 

 either mechanically or chemically ; mechanically by being 

 absorbed or occluded without combination, or cliemicaJly, 

 by forming chemical compounds, carbonates, or oxides. In 

 the case of the gunpowder above quoted, the oxygen is in 

 chemical combination with its carrier ; it forms an oxide of 

 nitrogen. As an example cf oxygen and carbonic acid 

 being held mechanically by their carrier, I may cite the 

 oxygen which exists dissolved or occluded, but not 

 chemically combined, in water, the oxygen which is 

 breathed by fishes, and the carbonic acid also contained 

 in the water of springs, rivers, and the ocean. These are 

 quite diflerent from the oxygen that is chemically com- 

 bined with the hydrogen to form the water. The latter 

 can only be separated by chemical violence, but the 

 mechanically dissolved or occluded oxygen and carbonic 

 acid may be pumped out or driven out by boiling the 

 water. 



Magnus proved experimentally that blood is capable of 

 absorbing a maximum of one and a-halt times its own bulk 

 of carbonic acid, and Magendie found that the venous 

 blood he examined in its ordinary condition contained 78 

 per cent, of carbonic acid, and arterial blood only 66 (by 

 volume). 



I may here describe an experiment that I devised for 

 displaying to a class at the Birmingham and ^Midland Insti- 

 tute many years ago, a visible illustration of the kind of 

 action that takes place in the conversion of dark venous 

 blood into bright red arterial blood by the action of oxygen. 

 I first added to a solution of the protosulphate of iron 

 (common green copperas) some carbonate of ammonia. 

 This threw down a dark carbonate of iron of nearly the 

 same shade as venous blood. Then to represent the lungs, 

 I spread some of this slimy precipitate over white blotting- 

 paper, and exposed it to the air. Oxygen was taken up, 

 carbonic acid given off, and the dark carbonate of iron con- 

 verted into blood-red sesqioxide. This experiment literally 

 supplies some colourable support to the theory that the 

 iron, which is a necessary constituent of the blood, is its 

 oxygen and carbonic acid carrier. 



My own view is that this change actually does occur in 

 the blood, and T maintain this conclusion on tho ground 

 that, as a matter of chemical fact, any solution of iron 

 or salt of iron exposed to the reducing agencies of the 

 venous blood, and to its carbonic acid and carbonates, must 

 be converted, as in my experiment, to a dark proto car- 

 bonate, and that such proto-carbonate exposed to the 

 oxygen of the air, as is the venous blood in the lungs, must 

 give off its carbonic acid, and become peroxidised and 

 blood-red. I say that this action must occur, but do not 

 say that it accounts for all the change. The total quantity 

 of iron is insufficient for this, and there are other reasons 

 that I must not further digress to state. 



Let us now return from this bye-path to the highway 



of our argument. Tho detour was made in order to find 

 an explanation of the cooling function of the skin where 

 evaporation fails. It is found, accordingly, if .some of the 

 carbonic acid with which the blocd in the capillaries is 

 charged passes off as a gas by simple expansive evolution ; 

 for it cannot thus expand from tho condensed to the 

 gaseous form without absorbing or using up a large 

 amount of heat or calorific energy, which heat it obtains 

 from its surroundings, and thereby cools them. 



1 sit in a cold room and lind that the previously- 

 described extra vascular tissue of my left hand is purple. 

 What must the blood in the superficial vcsf els have done to 

 become thus abnormally venous 1 It must have parted 

 with some of its arterial oxygen, and this must have com- 

 bined with some combustible carbon, and in becoming 

 venous, have helped to overcome the cooling influence 

 of the surroundings. If I now step into the hot chamber 

 of a Turkish bath, tho blood in these same vcsscLs will 

 become abnormally arterialised, brilliantly red ; i.e., it 

 will give off some of its carbonic .acid (by the cutaneous 

 respiration already described), aid thus cooperate with the 

 increased perspiration in pertbrniing the cooling function 

 of the skin. The same occurs in the paler tkin, but it is 

 not so visibly displayed. 



As I said at first, our artificial clothing should, as far as 

 possible, assi.st our natural clothing, the skin, by continuing 

 the same work that it performs ; therefore we require for 

 such clothing a material or materials that shall protect the 

 body from the cooling influence of the outer air when it is 

 colder than our bodies ; that shall have a cooling, or at 

 least a protecting influence, when we are exposed to higher 

 temperatures than blood-heat, and that .shall also allow free 

 transpiration of gases and vapoui-s. 



This last condition at once excludes all non-porous 

 material. The armour of our forefathers was detestable 

 clothing, and I am told that our Life Guardsmen would 

 rather go into action bare-breasted than with their breast- 

 plates — would prefer exposure to sword and bullet to the 

 depressing burden of such breast-protection. Waterproof 

 garments that are likewise air-proof arc similarly evil. 

 When I reach this jiart of the subject I shall point out the 

 distinction between waterproof and water-repellant material, 

 which latter need not resist the passage of the gaseous 

 exhalations cf the body. 



We are thus presented with a somewhat paradoxical 

 problem. We must find a material that will allow free 

 diffusion of gas or vapour, but will resist the passage of 

 heat, that will .shut in the subtle, imponderable, penetrating 

 radiations that travel with the inconceivable velocity of 

 light, and yet shall permit the slow, creeping diffusion of 

 aqueous vapour, carbonic acid, etc., of such extreme com- 

 parative grossness. 



We all know well enough how this is practically done ; 

 but the philosophy of the doing is by no means generally 

 understood. 



PHOTOGRAPHY AND MEDICAL 

 JUKISPRUDBNCE. 



By Willta5i Mathew. 

 THE DETERMINATION OF PERSONAL IDENTITY. 



IN all books dealing methodically with the topic of 

 medical jurisprudence, attention is directed to that 

 division of tho subject which treats of legal identifico,tion and 

 its related particulars. The rules and usages by which the 

 procedure is governed are primitive, but of long antiquity. 

 Whether btfore the accredited oflicer of the Crown — the 

 county coroner — or before the courts of criminal law, the 



