24 dr. davy's miscellaneous observations on the blood. 



The chief precautions taken were to receive the blood as it flowed from the 

 divided vessels of the animal killed into phials, immediately after they had been 

 emptied of water from which the air had been expelled by the action of the air- 

 pump, and after closing with a glass stopper, cooling the blood rapidly by im- 

 mersion in water. 



Though these precautions were taken, I believe they were not absolutely 

 necessary for good results, as I find that when water exhausted of air is poured 

 into a carefully washed phial from which water containing air has been poured 

 out, on submitting it to the air-pump, no air is extricated either from the water 

 or from the side of the phial. 



The experiments on exhaustion have been made on the blood of the common 

 fowl, of the duck, of the sheep, bullock, and pig ; they have most of them been 

 several times repeated. 



The results have varied more than I could have expected, tending to show 

 that the quantity of air extricable from the blood by the air-pump is far from 

 constant, and depends on circumstances, some of which are appreciable, others 

 obscure. 



1. From the blood of the common fowl, the quantity of air disengaged has 

 commonly been less than from that of the duck, sheep, bullock, and pig. 



2. The blood of all the animals, when taken from them shortly after feeding, 

 has commonly afforded more air than from animals of the like kind when fasting. 



3. Florid blood, which it may be inferred is chiefly arterial, has yielded less 

 air than dark blood, which probablj' is chiefly venous, and, accordingly, that 

 which flows first, when an animal has been blooded to death, less than that which 

 flows last. 



4. In a small number of instances, those of animals killed after a fast of many 

 hours, the fresh blood yielded no air. In some of the trials which gave this 

 result, the blood was mixed as it flowed with an equal quantity of water deprived 

 of air. 



5. In no instance have I witnessed the disengagement of air from fresh serum, 

 proving that the air, when extricated from the blood, is derived from the clot, 

 and it may be presumed, from the red corpuscles which are entangled in it. 



6. As might be expected, I have found the disengagement of air from the 

 action of the pump more copious in summer than in winter ; and also more copious 

 from blood, the fibrin of which has been broken up by having been agitated with 

 shot previously freed from adhering air, than from the clot left entire. In the 

 instance of the blood of the common fowl, which coagulates rapidly, affording a 

 firm coagulum, even the puncturing of it makes a difference ; air then escapes, 

 which before was retained. 



7. In many instances, blood which had yielded air on exhaustion, has, after 

 exposure for a few hours to the atmosphere, on repetition of the exhaustion, 



