FOODS — ANIMAL PRODUCTION. 081 



the ratio of inspired oxygen to respired carbon dioxid, was determined. 

 A tube provided with suitable valves was inserted in the trachea. The 

 dog eonld breathe only through this tube. The amount of inspired and 

 expired air was measured. The experimental methods followed are 

 reported in detail. 



The principal conclusions reached were the following: In normal 

 work all the Mammalia with which experiments have been made have 

 been found to require practically the same amount of chemical energy 

 for the unit of work. A little more than a third of the chemical energy 

 furnished by the food can serve for the production of external muscular 

 work. The rest is transformed into heat. When the work performed con- 

 sists in pulling, the proportion of the energy of the food which is effect- 

 ive is somewhat less than when the energy is expended in climbing an 

 incline, and the proportion decreases with increased work. The smaller 

 the animal the greater the energy required for forward progression of a 

 like mass through a like distance. The energy expended is very nearly 

 proportional to the surface area of the body. 



Contribution to the question of the source of muscular energy, 

 J. Frentzel (Arch. Physiol [Pfiiiger], 68, No. 5-7, pp. 212-221). — Two 

 experiments were made with dogs. In the first test the food furnished 

 an abundance of fat and protein. During the fust few days of the 

 second test the dogs consumed fat only and during the remainder they 

 fasted. The excretion of nitrogen in the urine under various conditions 

 of work and rest was determined. The amount of work performed was 

 measured as in the experiments by Zuntz, noted above (p. (580). The 

 amount of protein which was broken down in the body was computed 

 from the amount of nitrogen excreted in the urine. The energy which 

 this protein would furnish was also calculated. These values were com- 

 pared with the figures obtained by measuring the energy produced. 



The following deductions were drawn: When fat only is consumed or 

 when the subject is fasting, work is performed chietly at the expense of 

 the fat in the 1'ood or fat in the body. Using the data mentioned above, 

 protein could not be regarded as the sole source of muscular energy. 



Further investigations on the fat in muscular tissue, E. Bog- 

 danow {Arch. Physiol. [Pfliiger], 68, No. 8-9, pp. W8-430, figs. 3). — The 

 author has continued the work previously reported, 1 paying special 

 attention to testing the accuracy of the different steps in the method 

 followed in extracting and estimating the fat in meat. Experiments 

 were also made with frogs and rabbits to study the influence of mus- 

 cular work on the kind and amount of fat contained in the muscles. 



The conclusions drawn from earlier work are, in the author's opinion, 

 confirmed, namely, that muscular tissue contains 2 kinds of fat of 

 fairly constant composition, one which may be easily extracted with 

 ether and the other extracted with difficulty. The latter, the so-called 

 plasma fat, has a high percentage of fatty acid. Fat is regarded as 

 the immediate source of muscular energy. 



1 Arch. Physiol. [Pfliiger] 65, p. 81 (E. S. R., 8, p. 713). 



