THE BLOOD GASES 333 



which is evoked mainly by a diminished quantity of C0 2 in the blood as true 

 apncea, and that mediated by the vagus as false apnoea (Miescher). 



In asphyxiation and severe hemorrhage we meet with inhibitory effects upon 

 the respiratory mechanism which are of central origin. Both conditions agree 

 in that the supply of oxygen to the organs of the central nervous system and 

 the CO 2 removed from them are diminished. The consequence is, first a well- 

 marked dyspnoea, upon which follows, after a time, a period of apncea of greater 

 or less duration. This in its turn is interrupted by a series of new respiratory 

 movements (gaspings). Closer analysis of the apncea seen here shows that it 

 probably owes its origin to the action of some inhibitory mechanism upon the 

 respiratory center (Landergren). 



In certain diseases, in chloral narcosis and certain other forms of poison- 

 ing, and with pressure upon the medulla, etc., a special form of respiration is 

 observed, known after two English physicians as the Cheyne-Stokes respiration. 

 It consists of a regular rise and fall in the depth of the respiratory acts. No 

 positive explanation of the phenomena has yet been given. 



We have spoken so far of the respiratory center as a whole. Closer in- 

 vestigation, however, reveals that here, just as in the mechanism of degluti- 

 tion., we have to do with several functional centers bound together, the anatom- 

 ical relations of which are at present unknown to us, but the individuality 

 of which can be demonstrated by physiological experiments (Mosso). 



It is a fact by this time familiar to us that expansion of the thorax can 

 be accomplished either by the diaphragm or by the rib-lifting muscles. But 

 experiment has shown that in the same individual these two groups of muscles 

 do not always contribute toward the expansion of the thorax in the same ratio. 

 This appears most plainly in sleep, when respiration in man is essentially 

 of a costal type, whereas the diaphragm exhibits a certain paresis, in some 

 persons behaving like an inert membrane. In deep distress just the opposite 

 occurs: the diaphragm moves after the rib movements have ceased. These 

 and other observations to the same effect bear witness that the centers for 

 the rib-lifting muscles and for the diaphragm are to a certain extent inde- 

 pendent. Again, the centers which preside over the expiratory muscles are 

 independent; and finally, it has been shown that the respiratory movements 

 of the mouth and nose, as a rule, begin before those of the thorax, which is 

 evidence of the relative independence of the centers for those parts. 



THIRD SECTION 



THE BLOOD GASES 



As long ago as the middle of the seventeenth century, Robert Boyle 

 pumped a gas from the blood, and Mayow (1674) claimed that this gas 

 contained a substance called by him spiritus nitrocereus (oxygen). Likewise 

 Priestley demonstrated the presence of oxygen in the blood, and H. Davy 

 found carbon dioxide in it. These statements, however, were disputed by 

 others and only after Magnus (1838) had demonstrated beyond a doubt the 

 presence of oxygen, carbon dioxide and nitrogen in the blood, were the facts 

 generally accepted. 

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