DR. DAVY'S ACCOUNT OF SOME EXPERIMENTS ON THE BLOOD. 293 



me, that a very slight compressing force is sufficient to confine the air in the blood, 

 or rather, I should say, prevent its substance assuming the elastic state ; and further, 

 the probability, that the quantity of air so condensed is small. 



I have stated that in the majority of instances the indications of the disengagement 

 of air from blood in vacuo have been manifest. Exceptions, however, have occurred, 

 and those clear and decisive ; inducing me to believe that the quantity of air con- 

 densed in the blood is variable ; that there are times when it is in excess, and times 

 when in deficiency, and when totally wanting, connected with regularly changing 

 states of the functional system. I hope on another occasion to be able to recur to 

 this part of the subject, on which at present I have collected but a few facts. I may 

 add, that such facts tend in part to reconcile some of the discrepancies referred to in 

 the beginning of this section. 



V. Of the air or gases contained in the blood capable of being extricated by the air- 

 pump. 



As already mentioned, M. Magnus has stated that these gases are carbonic acid, 

 oxygen and azote in notable quantities. Taking the mean of ten of his experiments 

 on the blood of the Horse and Calf (five on arterial and five on venous), the total 

 quantity of the mixed gases he obtained was, in the instance of arterial blood, 10*4 per 

 cent, per volume, and in that of venous 7 6 per cent. ; the former consisting of about 



6*5 carbonic acid, 

 2*4 oxygen, 

 1*5 azote; 

 the latter of 



5*5 carbonic acid, 



\'\ oxygen, 

 rO azote. 



On a subject of so much importance, it is very desirable that the experiments of 

 M. Magnus should be repeated and verified ; for until this is done, considering the 

 physiological history of the blood, it will be difficult to avoid doubt, and to depend on 

 them with that degree of confidence which is justly due only to well-authenticated facts. 



The ingenious apparatus employed by M. Magnus being difficult of construction, 

 and not easily used excepting in a well-appointed laboratory, I must leave the repeti- 

 tion of his highly interesting experiments to those inquirers who are more happily 

 situated than myself for engaging in them. On the present occasion I shall limit 

 myself to the detail of some experiments instituted with a view of testing M. Magnus' 

 general results. 



As a solution of potassa has the property of absorbing carbonic acid gas, it follows 

 that if mixed with the blood previous to being subjected to the air-pump, it will prove 

 in some measure a test of the kind of air which the blood is capable of affording. 



With this intent two vials were prepared, the same as before used, one filled with 

 distilled water, the other with a weak aqueous solution of caustic potash, both care- 



