€54 EXPERIMENTAL INVESTIGATION OF THE ACTION OF MEDICINES. 



Hering,* who passed a stream of arterialised blood through the 

 vessels of the head while venous blood was circulating in 

 those of the body. The respiratory movements then ceased 

 exactly in the same way as if the whole blood in the body had 

 been perfectly oxygenated. When he reversed these condi- 

 tions, and passed arterialised blood through the body and 

 venous blood through the head, asphyxial convulsions took 

 place. This shows that the degree of activity of the respira- 

 tory centre in the medulla oblongata depends on the greater 

 or less venosity of the blood circulating through it, and not on 

 an irritating action exerted by venous blood on the ends of 

 afferent nerves in the lungs, or other viscera. 



The excitability of the respiratory centre may be greatly 

 modified : 1. By the temperature of blood in it ; 2. By the 

 action of drugs upon it. When the blood becomes warmer, 

 the excitability of the respiratory centre is greatly increased ; 

 the movements of respiration become much more vigorous, 

 and it is no longer possible, by the most active artificial 

 respiration, to produce a state of apnoea. Certain drugs, as 

 tartar emetic, or apomorphia, when injected into the veins 

 also prevent the production of apncea, but whether they do so 

 by increasing the excitability of the centre, or by acting as 

 irritants to it, is uncertain. 



Other drugs, such as chloral, greatly diminish the excit- 

 ability of the respiratory centre, so that the respirations 



* The request of a correspondent for a reference to Hering's experiments has, 

 fortunately, directed my attention to a mistake of some importance in this lecture. 

 I stated that Hering found that respiratory movements ceased when arterialissd 

 blood was passed through the head and renous blood through the body ; while, 

 on the contrary, asphyxial convulsions took place when venous blood was passed 

 through the head and arterial blood through the body. I ought to have said that 

 movements occurred in the blood-vessels such as would have taken place had the 

 same sort of blood which circulated through the brain been passing also through 

 the body. The experiments, however, were made on curarised animals, so that 

 respiratory movements were impossible. Hering had previously ascertained that 

 the arterial movements were synchronous with the respiratory movements, and 

 might, indeed, be regarded as caused by impulses proceeding from the respiratory 

 •centre. They might thus serve as indications of the condition of the centre, 

 where respiratory movements had been paralysed by curara. This paper is to 

 be found in the Wiener Acad. Sitzungsher.^ Math.-naturw. Classe, vol. Ix, 

 abth. 2, pp. 829-856. 



