52 



ANIMAL ELECTRICITY. LECTURE II. 



capacity containing i per cent, of carbonic acid, it is 

 unmistakeably altered. Thus it has reacted to a 

 hundredth of a cubic centimetre (or about one fiftieth 

 of a milHgramme) of CO,, and no doubt this has not 

 been a minimum Hmit. 



Fig. i8 (598).— Effect of expired air (Excitation by "little " CO.,). 



In conclusion let me place before you the record 

 of a complete experiment such as that of which you 

 have just witnessed an initial stage. Plate 589 is 

 an instance of the effect of expired air in an obser- 

 vation lasting about forty minutes. The series of re- 



