INVESTIGATIONS ON THE METABOLISM OF MILCH COWS 



Oscar Hagemann, Ph. D., 

 Professor at the Agricultural Academy, Poppehdorf, Germany. 



The theories concerning the processes in the animal body covered by 

 the term metabolism have undergone many changes, and although 

 much has been learned regarding them, they will undoubtedly be still 

 further changed as investigation progresses and methods are improved. 

 The earliest investigations of this sort were made with man. The 

 weight of the food and drink was determined, as well as the weight of 

 the material excreted in the urine, feces, and respiratory products. 

 These investigations were carried on by Sanctorius and published in 

 1614. 1 



Further progress was impossible until the science of chemistry 

 had been elaborated, and this required 150 years. The most impor- 

 tant advancement was in knowledge of the character of different gases. 

 Van Helmont (1G44) discovered carbon dioxid and also found that the 

 air expired by man and animals was injurious. In 1757 Black identi- 

 fied carbon dioxid in respired air. Priestly and Scheele discovered 

 oxygen in 1774-75; and Lavoisier established the relation between 

 oxygen and combustion, and in 1777 published his classic investiga- 

 tions, 2 showing that when the vital processes take place in the human 

 body oxygen is consumed and carbon dioxid excreted, in the same way 

 that combustion takes place in a furnace. He held the opinion that 

 with the aid of the food a fluid rich in carbon and hydrogen was 

 formed in the lungs. This was constantly renewed, and united with 

 the oxygen to form heat, water vapor and carbon dioxid being pro- 

 duced at the same time. Lavoisier also determined the effect of mus- 

 cular work, food, and low temperature on the consumption of oxygen. 



The investigations of Lavoisier and his associate, Sequin, may be 

 said to mark an epoch in animal metabolism. Levoisier's theory of 

 pulmonary combustion was incorrect, but more exact knowledge was 

 impossible at that time, since the fact that the animal body is made up 

 of cells was not discovered until many years after his death. 



We are still further indebted to Lavoisier for the methods of elemen- 

 tary analysis. Among other things, this rendered possible the deter- 

 mination of the elementary composition of the food, urine, and feces, 



1 De Medicina Statica Aphorisiini, Venice. 



2 Sur la respiration ties animaux et sur les changements qui arrivent n I'air en 

 passant par leur pounion. 



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