ELEMENTARY EXPERIMENTAL PHYSIOLOGY 195 



similar colour and the contrast between the appearance of an animal 

 killed by ordinary asphyxia produced by a blow on the head and one 

 killed by lack of oxygen due to carbon monoxide is very striking. 



Perform this simple and practical test for carbon monoxide. Kill two 

 animals, one by a blow on the head, the other by coal-gas. Cut open 

 their bodies and compare the colours of the viscera. Place a drop of 

 blood from each animal in separate test tubes, dilute with distilled water 

 and examine in good daylight. The blood containing carboxyhaemo- 

 globin can be distinguished easily by its cherry red colour ; it is more 

 pink and less yellow than the ordinary diluted blood. This test can be 

 confirmed by the examination of the two samples of blood with the 

 spectroscope (p. 346). 



The treatment of cases of carbon monoxide or coal-gas poisoning is to 

 give oxygen to increase the dissociation of carboxyhaemoglobin and to 

 keep the patient warm in order that his metabolism and the excitability 

 of his nervous system may be raised. 



CHAPTER LIII. 

 THE REGULATION OF RESPIRATION. 



THE ventilation of the lungs is regulated by a nervous centre in the 

 medulla oblongata. This can be proved by a series of experiments, in 

 which different portions of the central nervous system are destroyed. 



DEMONSTRATION. The medulla of an anaesthetised animal is 

 destroyed in the region of the calamus scriptorius ; respiration ceases 

 immediately and the animal dies of asphyxia. 



By experiments upon other animals it can be proved that destruction 

 of no other part of the central nervous system will produce this sudden 

 cessation of all respiratory movement. If the spinal cord be divided 

 close to the medulla the chief respiratory muscles will be paralysed, 

 but the movements of the nares will show that the centre is not 

 destroyed. 



The respiratory centre is influenced in two ways : (i) by the 

 composition of the blood which supplies it, and (ii) by nervous 

 impulses which affect its excitability. Experiments upon these points 

 can be performed by the student upon himself; he can alter the 

 composition of the air in his lungs and thus affect the gaseous 

 composition of his blood. 



Influence of breathing air containing carbon dioxide. The subject 

 of the experiment breathes air through a mask and valves and the 



