272 RESPIRA TION 



presence of the peroxide (p. 76). As regards the activity of this 

 ferment, blood comes first; then follow spleen, liver, pancreas, 

 thymus, brain, muscle, and ovary. It is present in the blood-free 

 organs as well as in the blood. Some tissues, both animal and 

 vegetable, contain a ferment, .an oxydase, which causes the oxida- 

 tion of guaiaconic acid in the presence of atmospheric oxygen, and 

 these do not need peroxide of hydrogen in order to render guaiacum 

 blue. An allied ferment which also induces the blue colour in 

 tincture of guaiacum is the so-called laccase found in the most active 

 form in the latex of the tree from which Japanese lacquer is ob- 

 tained, but also in many other plants. Many fungi contain a fer- 

 ment, tyrosinase, which oxidizes tyrosin, and in certain animals 

 tyrosinases have also been demonstrated. Another well-known 

 oxidizing ferment in fresh animal tissues is characterized by the 

 property of forming indophenol by oxidation in an alkaline solution 

 of paraphenylenediamin and a-naphthol, and may therefore be 

 termed indophenyloxydase. The colourless solution becomes 

 reddish or violet. This ferment is contained in pancreas, salivary 

 glands, spleen, thymus, and bone marrow, but has not been de- 

 tected in muscle, lungs, brain, kidneys, and other organs. It is 

 to be expected that other oxydases capable of favouring oxida- 

 tion of specific kinds of food substances or their decomposition 

 products will be discovered, but it ought to be remarked that 

 those at present known are only capable of attacking relatively 

 simple organic substances, and it would be rash to conclude 

 that this is the only way in which living protoplasm can bring 

 about the rapid, but at the same time the regulated, oxidation 

 which is so characteristic a feature of its activity. Yet the capacity 

 of the cell to regulate the intensity and the extent of the intra 

 cellular oxidations would seem to find a simple explanation if we 

 assign an important role to oxidizing ferments formed by the cell 

 itself in accordance with its needs. In this connection we may 

 mention a ferment, aldehydase, which was formerly included 

 among the oxydases, but is now known to be a hydrolytic enzyme. 

 It splits aldehydes so as to yield the corresponding acid e.g., 

 salicylic aldehyde is split into salicylic acid and saligenin. Evidence 

 of its presence in most organs has been obtained. 



The Passage of Carbon Dioxide from the Tissues into the Blood. 

 Since nearly the whole of the carbon dioxide eventually found in 

 the blood is formed in the tissues, and only a small amount in the 

 blood itself, it might be supposed that the partial pressure of the 

 gas in the tissues would necessarily be greater than in the blood. 

 This would certainly be true if the whole of the carbon dioxide 

 was transported in the form of dissolved gas. This, however, is 

 not the case. Much of it is combined, and as the proportion of 

 free to combined carbon dioxide in the blood is variable, it may be 



