-400 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS sufficient elimination of uncontrollable factors, and physiological test conditions. The apparatus is also suitable for batch tests. Figure oe Respiration apparatus There are a variety of problems where it is necessary to establish the influence of the sample upon the basic metabolic rate, the oxygen consump- tion, and the carbon dioxide exhalation. For these purposes an apparatus, illustrated in Figs. oe, 8, and 4, has been developed which, in particular, en- ables us to establish data on the energetic changes of the organism, i.e. the amounts of oxygen inhaled and of carbon dioxide exhaled, serve as para- meters of the metabolic physiology of the test organism. The accuracy of this apparatus is very satisfactory. The error in the measurement of COs is of the order of 1.1-1.6 per cent of the value read off. With oxygen the error is considerably less because it only reflects instru- mental errors.

INHALATION AND TOXICITY STUDIES 401 E. ' ,f Figure 3 Testing chamber If administration to individual animals is desired another experimental device (Figure 5) developed in our laboratories can be used. Every animal is fixed in this device after the appropriate acclimatization to these conditions. The test material is administered to each animal in- dividually by means of a pharyngeal or tracheal probe, or through a mask, the duration and frequency of the application can be regulated centrally. This apparatus is valuable for testing the effectiveness of pharmaceuticals. which are absorbed as aerosols via the mucous membrane of the mouth or respiratory tract. In such experiments the test aerosol must enter the respiratory tract as unaltered as possible, and it is essential that the mount can be measured very accurately. Often it is impossible to select a definite species of animal without preliminary trials. Nor is it advisable to restrict the tests to only one species. The small rodents, for instance, offer the advantage of a relatively