Animal nutrition / [Thomas Barlow Wood].

  • Thomas Barlow Wood
Date:
1924
Catalogue details

Licence: In copyright

Credit: Animal nutrition / [Thomas Barlow Wood]. Source: Wellcome Collection.

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    Chapter XXI. The direct and indirect methods have been found to give identical results. The indirect method possesses many advantages for the measurement of the heat required for muscular work, because it can be used for animals working in natural conditions. It is obviously impossible for a horse, for instance, to work normally inside a calorimeter. The method of experimenting by indirect calorimetry with the horse is first to perform the operation known as trache¬ otomy, by means of which a tube is permanently fixed in the trachea, or windpipe, as it is commonly called. To this tube is attached a rubber tube connected with an expanding air¬ tight bag, which can hold several hundred litres of expired air. The bag is fixed on the horse’s back, and at the beginning of each experiment is completely collapsed. The rubber connecting tube is provided with a three-way stop cock, which, when turned one way, connects the trachea with the open air, so that the animal does not breathe into the bag, but when turned through one right angle connects the trachea with the bag, which is then filled with the expired air. When the stop cock is turned through two right angles the bag is closed, and the animal again expires into the open air. There is also in the connecting tube a valve which admits the inspiration of fresh air, but directs the expired air into the bag. The apparatus having been fixed in position, the animal is allowed to rest for some time. Whilst the Resting animal is still at rest the stop cock is turned so that the expired air nows into the bag and kept in this position for a time accurately measured by a stop watch. The stop cock is then turned, and the bag detached, a small measured sample of expired air taken from it for analysis, and the rest forced out through a gas meter so as to ascertain its volume. In analysing the sample of air the carbon dioxide is absorbed by potassium hydrate solution, the decrease in volume giving the volume of carbon dioxide. The oxygen is then absorbed by alkaline solution of
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