between the source of light and the prism, two dark bands will appear (Fig. 18) in that part of the spectrum previously occupied by the yellow ray, and more particularly in that portion of the yellow ray adjoining the orange and green rays, the two dark bands being separated by that part of the yellow ray still transmitted through the blood. If the arterial blood be now replaced by venous blood, or simply deoxidized, as can be done by appropriate means, the two dark bands will disappear, and in that part of the spectrum where the yellow ray was transmitted there will appear one dark band, while that part of the spectrum lying on either side of the dark band will be occupied to a small extent by the yellow ray. By means of the spectroscope not only can a suspected material be proved to be blood and arterial distinguished from venous blood, but blood in general can be distinguished from that which has absorbed carbonic oxide gas, as also from solutions of acid alkali and reduced hæmatin, the dark bands presented by their spectrum being different in each instance (Fig. 18). The spectroscopic method is the most convenient, reliable, and delicate of the different methods which have been described for investigating bloodstains.

The spectroscope employed in medico-legal examinations is the same as that used in chemical and physical researches, the essential parts being shown in Figure 19, or it may consist simply of a spectroscopic attachment to a microscope. The delicacy of the spectroscopic method of investigating blood-stains is such that a solution consisting of one grain of hæmoglobin, upon which the absorption of the light depends, to a pint of water will interfere with the transmission of strong sunlight sufficiently to render the two dark bands visible. It thus becomes pos

sible, by means of a spectroscope, to state positively that stains years old on wood, linen, or iron, even when found in a putrid condition, were made by blood. It is true that the spectra of solutions of the coloring matter of the petals of cineraria,' of cochineal, madder, and other red dyes, present dark bands in their spectrum, but their situ

ation is either not exactly the same as those of the blood spectrum, or they can be distinguished from those of the latter by the action of ammonia and potassium sulphate.

The spectroscopic method of investigating blood-stains, reliable and delicate though it may be, does not enable the examiner to state that a suspected material is human blood, but only blood. By none of the methods, therefore, of examining blood-stains, whether chemical, microscopic, or spectroscopic, can human blood be distinguished positively from that of other animals.

Coagulation of Blood.-One of the most remarkable properties of the blood is its power of separating into clot and serum, due to the coagulation and subsequent shrinkage of its fibrin (Figs. 20, 21), the process being com

1 Of the different menstrua used by the writer to obtain the coloring matter from the petals of cineraria, glacial acetic acid was found to be the best.

pleted outside the body within a period of from 10 to 12 hours.

Conditions Influencing Coagulation of Blood.-While the blood does not usually coagulate in the living body, it almost invariably does so in the dead body, and within a period varying between 12 and 24 hours. There are various conditions which influence the coagulation of the blood within and without the body, some of which are better understood than others. Only those conditions influencing coagulation which may have an importance from a medico-legal point of view need be here considered. Blood flowing from a small orifice coagulates more quickly than when flowing from a large one; more quickly when it is received into a shallow rough vessel than when in a deep smooth one. The coagulation of the blood is retarded or even prevented when mixed with solutions of sodium sulphate and carbonate. Rapid freezing will prevent the coagulation of the blood; blood so frozen will, however, coagulate if carefully thawed. A temperature of from 32° to 140° F. favors coagulation. The menstrual blood is kept in a more or less fluid condition by the vaginal secretions.

The medical expert is often asked to express an opinion as to how much blood the body of the deceased contained. While it is impossible to state exactly how much blood there is in any human body, it may be said that on an average there is one pound of blood for every eight pounds of body-weight; that is, there would be about six

teen pounds of blood in the body of a man weighing one hundred and twenty-eight pounds. This estimate is based upon the fact that twelve pounds of blood were collected during the execution by beheading of a criminal weighing one hundred and twenty-eight pounds, and that four pounds of blood were obtained after the execution by washing out the blood-vessels.

CHAPTER VI.

Burns and Scalds-Death from Suffocation by Strangulation-Hanging -Drowning.

A BURN may be defined, medico-legally, as an injury produced by the application of a heated substance to the surface of the body, while a scald results from the application of a liquid at about its boiling-point. The effects of burns and scalds upon the body are essentially the same. Burns vary in their intensity from a mere redness of the skin to a complete carbonization of the body.

The danger from burns depends more on their extent than upon their depth. This is due to the fact that the excretory and heat-regulating functions of the skin are interfered with in proportion to the extent of the skin involved.

It may be stated, as a general rule, that if one-third of the body, or even one-third of the skin, be severely burned, the burn will probably prove fatal. Death in the case of burns is usually due to shock, though often caused by suffocation, exhaustion, or gangrene. It must be remembered, however, that the result of burns will be very much influenced by the age and constitution of the individual and the part of the body affected. Thus, for example, burns are more dangerous in the young than in the old; more so on the trunk of the body than on the limbs; more so if in separate patches than when continuous, supposing the parts burned are of equal extent.

The post-mortem appearances observed in cases of death