268 RESPIRATION 



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 <z-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. 



SECTION VI. RELATION OF RESPIRATION TO THE NERVOUS 



SYSTEM. 



The Respiratory Centre and its Connections. Unlike the beat of 

 the heart, the respiratory movements are entirely dependent on the 

 central nervous system. The ' centre ' which presides over them is 

 situated in the spinal bulb. It is a bilateral centre that is, it has 

 two functionally symmetrical halves, one on each side of the middle 

 line. Each of these halves has to do more particularly with the 

 respiratory muscles of its own side, for destruction of one-half of 

 the spinal bulb causes paralysis of respiration only on that side. 

 Anatomically the respiratory centre has not been sharply localized, 

 but it lies lower than the vaso-motor centre, not far from the point 

 of the calamus scriptorius. Stimulation of this region during apncea 

 (p. 277) is stated to cause co-ordinated inspiratory movements and 



