IN ARTERIAL AND VENOUS BLOOD. 543 



greater in the venous than arterial blood of 

 carnivorous than of herbivorous animals, it 

 must also be given off in the air cells of the 

 lungs, whether it unites with oxygen to form water 

 or not. And if there be more nitrogen in the ar- 

 terial than venous blood of animals, it must be 

 derived from the atmosphere by respiration. 

 But so far has this department of Organic Che- 

 mistry been neglected, that no one has ever at- 

 tempted to ascertain the relative proportions of 

 oxygen, carbon, hydrogen, and nitrogen, in the 

 venous and arterial blood of different animals, 

 with the view of discovering the true theory of 

 respiration. The consequence of thus rejecting 

 a whole series of facts has been, that nearly 

 everything most important to be known, remains 

 still involved in deep obscurity, or vitiated by 

 fallacious hypotheses. 



That there is more hydrogen in the chyle of 

 carnivorous than of herbivorous animals, would 

 appear from the researches of Dr. Marcet, who 

 found that when taken from the thoracic duct of 

 dogs nourished for several days on animal food 

 alone, it presented a milky appearance, and af- 

 forded an oily, opaque substance, that rose to the 

 surface like cream. When separated and kept for 

 some time, it assumed the consistence of soft 

 butter ; it also decomposed much sooner, and af- 

 forded a larger proportion of ammonia than chyle 

 taken from the horse, which was transparent and 



