ADVANCED EXPERIMENTAL PHYSIOLOGY 149 



by carbon monoxide is pink or cherry red. The blood in the viscera 

 has a 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 carboxyhaemoglobin 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 examina- 

 tion of the two samples of blood with the spectroscope. 



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

 is to give oxygen to increase the dissociation of carboxyhaemo- 

 globin and to keep the patient warm in order that his metabolism 

 and the excitability of his nervous system may be raised. 



CHAPTER XXVIII 

 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 experi- 

 ments, in which different portions of the central nervous system 

 are destroyed. 



DEMONSTRATION. The medulla of an anaesthetised mammal 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 des- 

 truction 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 sub- 

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

 the ventilation of the lungs is determined by a meter. Then, 

 unknown to the subject, the air to be breathed is taken from a gas 

 bag containing air with 3 or 4 per cent, of carbon dioxide. The 

 breathing is increased. Carbon dioxide stimulates the respiratory 



