246 MASS. EXPERIMENT STATION BULLETIN 188. 



into the trachea and measuring at intervals the intake and outgo of the 

 respiratory gases. 



(d) The Respiration Calorimeter. — The apparatus consists of an air- 

 tight room in which the animal is placed for different periods of time, and, 

 in addition to collecting the feces and urine, the carbon dioxide exhaled 

 and the heat radiated are accurately measured. It has been employed 

 particularly in nutrition experiments with man, neat cattle, dogs and even 

 smaller animals. 



An illustration of the value of the calorimetric method over chemical an- 

 alysis and digestibility may be cited in the experiment conducted by Wolff, 

 who found that a horse weighing 500 kilograms (1,100 pounds) required 

 6 kilos of oats and 6 kilos of hay, equivalent to 5,547 grams of digestible 

 organic nutrients (minus fiber), to keep him in a state of maintenance and 

 to enable him to perform 1,450,000 kilogrammeters of work. Of these 

 nutrients 3,551 grams were necessary for maintenance, leaving 1,996 grams 

 available for work. This amount — 1,996 grams — is equivalent to 

 3,478,030 kilogrammeters of work (1,996 multiplied by 4.1 calories equals 

 81,836 calories, which, multiplied by 425, equals 3,478,030), whereas the 

 work actually performed was 1,450,000 kilogrammeters, or 41.7 per cent. 

 Even this percentage was found by other experimenters to be too high, 

 and is explained on the ground that the horse was particularly accustomed 

 to such work. Ziintz and Lehmann, by the use of the respiratory quotient, 

 found that the percentage of similar work in relation to digestible nutrients 

 was reduced to 26 per cent., and Laulonie, by the same method, secured 

 22 per cent. In other words, after the maintenance requirement is satis- 

 fied, the horse seems to be able to make use of about 25 per cent, of the 

 remaining energy in the form of a definite kind of work (net efficiency of 

 the animal, Armsby). 



It has been found further by Ziintz and Hagermann, in an extended 

 series of experiments, that the net efficiency of food in case of the horse 

 varies widely, depending upon the character of the work performed. Thus, 

 in case of walking without a load, the average efficiency was 35 per cent.; 

 in different grades of ascent, at a walk without a load, from 33.7 to 36.2 per 

 cent.; and with a load, 22.7 per cent. In case of work at a slow trot with- 

 out a load the net efficiency was 31.96 per cent., and with a load, from 23.4 

 to 31.7 pet" cent. On the basis of these studies formulas have been worked 

 out for the amount of food required for definite kinds of work, but it is 

 hardly practicable to employ them under conditions ordinarily prevailing. 



By this method of procedure Ziintz has determined the net energy value 

 of a number of foods for the horse, and the results have led to a reduction 

 in the amount of coarse food supplied, and an increase in the amount of 

 concentrates, thus requiring the animal to expend less energy in mastica- 

 tion and digestion, and to care for less inert matter in the intestinal tract. 

 A former ration for the bus horses of Paris, composed of oats, corn, beans, 

 bran, hay and straw, contained 18.5 kilos of dry matter, while a ration 

 based on the results of recent investigations, composed of oats, corn, beans. 



