204 THE AMERICAN MONTHLY [September, 



ten but a score of years since, is now of little value, and tends to con- 

 fuse rather than enlighten one seeking to obtain reliable information. 



Not many years ago it was claimed by some that human blood could 

 be distinguished from that of all animals by haemin crystals, and ex- 

 perts have so testified. This is now used only as a corroborative test 

 in determining the substance to be blood. The physical appearance 

 of a blood stain varies with its age and the material upon which it is 

 found. Blood which has dried upon a polished or smooth surface, 

 such as steel, glass, varnished wood, and such textile fabrics as silk or 

 satins, rapidly assumes a dark brown color. When it happens that the 

 stains are on mahogany or walnut furniture, they are sometimes very 

 difficult to detect by daylight, though easily distinguished by the dim 

 reflected light of a candle. On white pine and other soft woods it re- 

 tains its bright red appeai'ance for a considerable period. 



The first step in the examination of a suspected stain is to ascertain 

 whether it is blood or not; and if blood, next to determine, if possible, 

 its source. These two problems can best be solved by aid of the mi- 

 croscope and micro-spectroscope. For die purpose of diagnosing the 

 kind of blood, the microscope alone is available. The prevailing 

 opinion among experts is that the finding of corpuscles is the only re- 

 liable evidence which should be admitted in criminal cases. Blood 

 corpuscles are not liable to be confounded with any other known ob- 

 ject by a person familiar with their appearance, vet careless mistakes 

 have occurred. In Ohio I was once called upon to make an examina- 

 tion of a stain for the purpose of corroborating evidence already intro- 

 duced to the effect that it was blood. All ordinary methods failed to 

 reveal blood corpuscles, and other tests proved conclusively that it was 

 another substance. On examining the slides prepared by the witness 

 who had previously testified with his own instrument, I was surprised 

 to find that what he had mistaken for blood corpuscles were nothing 

 but spots left from condensed moisture on the lower lens of his eye- 

 piece, he never having had the object itself in focus during his investi- 

 gation. Such a blunder could not happen to one familiar with micro- 

 scopical manipulation, as a mere turning of the eye-piece, which is 

 generally done from habit, would have exposed the error. 



The red corpuscle of human blood is a small, circular, non-nucleated, 

 biconcave disc. The same form and appearance exist in most of die 

 mammalia, the only means of distinguishing between the two being 

 their difference in size. The red corpuscle in man averages about 

 3^Vq °f an ' ncn m diameter. Race, habit, and environment seem 

 to have no effect on the size or appearance of these discs. The late 

 Dr. J. G. Richardson, of Philadelphia, during the Centennial Exhibi- 

 tion held in that city in 1876, examined and measured one hundred 

 corpuscles from each of fourteen persons of different nationalities, and 

 found their average diameter to be -3 g^T °f an i nc b- Selected corpuscles 

 may measure more and others less, and for this reason it is impossible 

 to determine with absolute certainty human blood from that of some 

 animals. 



Unfortunately, in the dog, one of our most common domestic pets, 

 the corpuscles so closely resemble those of man that it is difficult to 

 distinguish between them. Out of two hundred corpuscles from the 

 blood of a man and an equal number from a dog, Dr. J. P. Treadwell 



