214 



NUTRITION OF FARM ANIMALS 



The principle of the Pettenkofer apparatus has also been very 

 extensively used for the investigation of the pulmonary exchange, 

 especially by Zuntz and his associates, 'to whom the development of 

 this form is largely due. Figure 30 shows a horse equipped with a 

 tracheal cannula for experiments with this type of apparatus. Ow- 

 ing to the fact that the excretory gases are not diluted with many 

 times their volume of air, as is the case when a respiration chamber is 

 used, the results are much sharper and it is possible to determine 

 the amount of oxygen consumed as well as that of carbon dioxid 

 given off. 



FIG. 29. The Mockern respiration apparatus. (Bailey's Cyclopedia of Ameri- 

 can Agriculture.) 



300. Investigation of pulmonary exchange. For many pur- 

 poses a determination of the gaseous exchange in the lungs, 

 either with the Regnault-Reiset or the Pettenkofer type of 

 apparatus, is preferable to determinations of the total exchange 

 in a respiration chamber. The former method is especially 

 adapted for short experiments. By its use, it is possible to 

 trace sharply changes in the amount of the metabolism, the 

 respiratory quotient, etc., produced by the administration of 

 feed substances, drugs, etc., by experimental lesions, and es- 

 pecially by work, changes whose amounts would often be 

 relatively very small as compared with the total excretion for 

 24 hours as measured in the respiration chamber and which, 

 therefore, if they did not escape detection altogether, could not 

 be as accurately determined either quantitatively or chrono- 

 logically. On the other hand, it is impracticable to continue 

 its use through long periods, a day, e.g., and since it takes 



