914 EXPERIMENTS OF EDWARDS, 



and puppies, living on milk, (which contains 

 much more nitrogen than vegetable food,) than 

 was absorbed, that the same was true of adult 

 sparrows, during spring, summer, and autumn, 

 until the 22nd of October ; after which time, 

 there was a striking disappearance of nitrogen ; 

 and that when yellow hammers were kept fifteen 

 minutes in a vessel containing 94*6 cubic inches 

 of air, during the latter part of autumn, winter, 

 and the beginning of spring, the amount of nitro- 

 gen was diminished in almost every instance. 

 Now although Dr. Edwards does not notice the 

 fact, it is well known, that sparrows, yellow ham- 

 mers, and most of the smaller birds, live to a con- 

 siderable extent during the warmer months, on 

 worms and insects, that afford, like milk and other 

 animal matter, a much larger amount of nitrogen 

 than grain, which forms the principal nourishment 

 of birds after the middle of October, when their 

 summer food is destroyed by the cold season. We 

 are therefore authorised to conclude, that when 

 animals live on vegetable food, which contains 

 less nitrogen than is requisite to form blood, the 

 deficiency is obtained from the atmosphere by 

 respiration,* as shewn by the experiments of 

 Priestley, Spallanzani, Humboldtand Provencal, 

 Davy, Henderson, and Pfaff: but that when 



* It is during the passage of chyle, venous blood, and the 

 waste materials of the solids through the lungs, that the whole is 

 converted into arterial blood, by giving off carbon and hydrogen ; 

 and by absorbing nitrogen from the atmosphere, whenever that 



