Pohl, and arsenious acid by Spitzer, for the same purpose. The most important of the oxydases of the animal organism is the one named salicylase by Abelous, which oxidises salicylic aldehyde to salicylic acid, and it occurs in most of the organs of the animal body.

Medvedeff, who has investigated the oxidising action of liver extracts on salicylaldehyde, states that the amount of oxidation is proportional to the square root of the concentration of the aldehyde, since this is the proportion of the substance dissociated in solution, but directly proportional to the concentration of the ferment.

According to Abelous and Biarnès, oxygen is consumed and carbon dioxide is liberated when salicylic aldehyde is oxidised to salicylic acid by liver extracts.

Spitzer has been able to convert the nuclein bases into uric acid by extracts of the liver and the spleen in the presence of air which was bubbled through the solution, putrefaction being carefully excluded; xanthine and hypoxanthine were almost quantitatively converted into uric acid; adenine and guanine, however, were oxidised to a lesser extent.

A third oxidising ferment, according to Abelous and Biarnès, has no action on salicylic aldehyde, but turns guaiacum tincture blue.

Cavazzani infers the existence of an oxidising ferment -cerebro-spinase-in the cerebro-spinal fluid, as it gives with pyrogallol and sulphuric acid a crystalline deposit of purpurogalline; with tannic acid it gives a brown, with quinol a rose colouration, and with o-toluidine a roseviolet precipitate.

The disappearance of sugar from blood which has been

shed, is another case of oxidation in animal tissues. Seegen has shown that it is not caused by micro-organisms, as the same process takes place in the presence of chloroform; it is due to a glycolytic ferment produced by the leucocytes, or white blood corpuscles, and it exists not only in blood, but in various organs. It is not yet definitely known what change the sugar undergoes: the experiments of Oppenheimer have led to no definite conclusions, since he could not detect alcohol or acetone, though he obtained traces of iodoform; nor as yet has he been able to prove the formation of lactic acid, which is very probably produced in the process.

The light-producing organs and the eggs in the ovary of the female glowworm give a blue colour with guaiacum tincture. Dubois considers that the active agent in the production of light is an enzyme which he has named luciferase, but he believes it is not a result of oxidation.

Waters rich in iron in the form of ferrous hydrogen carbonate, contain several species of micro-organisms, which are able to oxidise this compound after it has passed by osmosis through their cell-walls, and convert it into ferric hydroxide with the evolution of carbon dioxide, thus:

2FeH2(CO3)2 + H2O + 0 = Fe2(OH)6 + 4CO2

This change can be followed in the deposited layers in the sheaths of these microbes. At first they are pale yellow, and can be decolourised by water containing carbon dioxide; but later on they become brown-red, and are only decolourised by dilute hydrochloric acid; finally this reagent cannot decolourise them. We have to thank Winogradsky for the majority of the investigations upon

these iron bacteria, which can only grow when ferrous carbonate is present, ferric oxide even being useless as a form of iron. Molisch states that manganese can replace the iron. The deposits of ferruginous ochre and bog iron ore are said to be the result of the action of these bacteria.

Hydrogen sulphide in well-waters is oxidised by the sulphur bacteria to sulphur, in accordance with the equation

oxygen being necessary for this transformation. This change was definitely shown in 1886 by Winogradsky, and further investigations were carried out by Jegunow, who has shown that the sulphur in a higher level of the bacterial cell is oxidised to sulphuric acid, which is excreted. The reverse process of reduction of sulphates will be described in the next chapter.

CHAPTER XII.

CHANGES OCCURRING AS THE RESULT OF REDUCTION.

DE REY-PAILHADE, in 1889, observed that hydrogen sulphide was formed from sulphur, when it was mixed with yeast, and he attributed this change to the action of a reducing enzyme, which he termed philothion. Sostegni and Sannino have obtained the same result; they added flowers of sulphur to a solution of sugar, which was fermented with a pure cultivation of yeast, and found that hydrogen sulphide was evolved. Salkowski has noticed the production of hydrogen sulphide in wine, but he attributes its formation to the action of bacteria on the sulphur compounds present in it.

Philothion, sometimes alone and sometimes with laccase, has been found by De Rey-Pailhade to be contained in germinating seeds; he has shown that it contains a proteid radicle which can enter into loose combination with manganese or hydrogen in the same way as Bertrand showed in the case of laccase.

The power possessed by philothion, of forming hydrogen sulphide from sulphur, is stated by Cossettini to be lost when it is filtered through a Chamberland filter, and Pozzi-Escot finds that philothion does not give the blue colour with guaiacum tincture and hydrogen peroxide,

which is the usual test for these enzymes. Hydrogen peroxide, however, is decomposed with the evolution of

oxygen.

This observer identifies philothion with catalase, an enzyme stated by Loew to be of universal occurrence, and to whose presence the power of decomposing hydrogen peroxide, possessed by all enzymes, is due; this observer states that catalase exists in an insoluble and a soluble form, termed a- and B-catalase respectively.

Pozzi-Escot finds that philothion can also cause the hydrogenation of selenium and phosphorus, but not, or only very slightly, of tellurium and arsenic.

The production of hydrogen sulphide by micro-organisms has been investigated by Zelinsky, who isolated a bacterium-Bacterium hydrosulfureum ponticum—from the ooze at the bottom of the Black Sea; it can produce hydrogen sulphide not only from proteid matter, but also from inorganic salts, such as sulphates, sulphites, thiosulphates, and even ammonium thiodiglycollate when they are added to the nutrient medium. Vibrio hydrosulfureus is shown to be active in the same way. Beyerinck has also obtained a micro-organism which transforms sulphates into hydrogen sulphide; but Saltet finds that this Bacillus desulfuricans only partially reduces sulphates to sulphites or other oxygenated sulphur compounds which are then reduced by other bacteria to hydrogen sulphide. The cycle which sulphur compounds undergo in nature is thus completed; for in the previous chapter (Chapter XI.) the oxidation changes which sulphur underwent were briefly described.

Compounds of arsenic, in wall-papers especially, are