MEMORANDA. 283 



direction. The microscope was found to be of great value, 

 when first introduced, in showing, by the form of the blood- 

 corpuscles, the class of animals whence the blood came ; and 

 even now it can hardly be dispensed with, inasmuch as the 

 aj^pearances which it discloses are characteristic, and can be 

 made to last for some time. Further, it introduces* no fallacv 

 into the test. A few years later, the discovery of blood- 

 crystals of definite shape and reactions led observers to believe, 

 not only that this was a test more delicate than that which 

 the corpuscles afforded, but that, by noting the different 

 crystalline forms, we might ascertain the animal from which 

 it came, or at least distinguish the blood of man from that of 

 other mammals. Observation, however, proved the incorrect- 

 ness of this view ; and also that, in cases where there was a 

 mere stain, the test was inapplicable. The process, too, was 

 one of by no means easy application. 



The next advance was made by examining the blood-solu- 

 tion by means of the spectroscope, and noting the position of 

 the dark bands in the green portion of the spectrum. This 

 process has the advantage of dealing with very minute quan- 

 tities ; but it requires considerable practice and a good deal of 

 scientific knowledge to be certain of the result. 



A simpler test, and one easy of application, has been lately 

 devised by Dr. Day, of Geelong. It consists in the addition 

 of tincture of guaiacum and " ozonized ether " to a weak solu- 

 tion of blood, when a bright blue colour is produced. 

 Schonbein, it will be remembered, first described accurately 

 the existence of two differently active states of oxygen, called 

 ozone and antozone. A molecule of oxygen may, in this view, 

 be looked upon as neutral or passive, and formed by the union 

 of a negative and positive particle. Ozone, as is well known, 

 is supposed to be found in atmospheric air, in certain electrical 

 conditions ; and it may be produced by passing currents re- 

 peatedly through a tube containing oxygen. Some inorganic 

 bodies, as the peroxides of manganese, lead, and potash, con- 

 tain oxygen in the state of ozone ; others, as the peroxides of 

 hydrogen and barium, are supposed to be in an opposite 

 state, and to contain antozone. Ozone has an oxidizing in- 

 fluence on guaiacum resin, and turns it blue, and thus differs 

 from antozone, which has no effect on it. Further, antozo- 

 nides differ from ozonides, in converting red chromic acid 

 into blue perchromic acid. Van Deen many years ago drew 

 attention to this subject, but Dr. Day has more fully Avorked 

 it out. See a paper on "Allotropic Oxygen " in the 'Austra- 

 lian Medical Journal,' May, 1867. When tincture of guaiacum 

 is exposed to air or oxygen, it becomes blue ; and this change 



VOL. VIII. NKW SER. X 



