The conclusions drawn by Dr. Girtanner from his experiments are, 1. That the change of colour which the blood undergoes during the circulation is not owing to its combination with hydrogen air[68]. 2. The deep colour of the blood in the veins is owing to the _carbon_ it contains. 3. That the vermilion colour of the arterial blood proceeds from the oxygen with which the blood is conjoined during its passage through the lungs. 4. That respiration is a process exactly analogous to the combustion and oxydation of metals; that these phenomena are the same, and to be explained in the same manner. 5. That, during circulation, the blood loses its oxygen, and charges itself with _carbonic hydrogen_ air, by means of a double affinity. 6. That, during the distribution of the oxygen through the system, the heat which was united with this oxygen escapes; hence the animal heat. 7. That the great capacity of arterial blood for heat is owing to the oxygen with which it is united in the lungs. [68] Here it is necessary to observe, for the sake of accuracy and perspicuity, that, in the new chemistry, the terms of which are now very generally adopted, the words _oxygen_ and _hydrogen_ when mentioned by themselves are not understood to signify any kind of air, but what I have called the condensable part of the air. If the word _air_ is added, then the whole substance of the fluid is understood. But though this is the strict orthodox language of the new chemistry, it is impossible to say whether every one who adopts the terms be sufficiently careful in this respect. Indeed this is one out of many inconveniences that might be pointed out which have arisen from this nomenclature; for thus the mere omission of a monosyllable, which may happen in numberless instances, totally perverts the meaning of the author, and may of course subject him to unmerited censure. Besides, it is not to be known, unless the author tells us so, that he designs to observe this strictness, and of consequence we must in multitudes of cases be uncertain of the meaning of what we read. Thus, in the present instance, when Dr. Girtanner speaks of _oxygen_, we know not certainly whether he means the air in substance, or only one of its component parts. Probably he means the condensable or solid part. If he does so, there must be a very material difference between his theory and that laid down in the Encyclopædia, and which is supported throughout this treatise. In the latter it is maintained that the condensable part is thrown out by the breath, being previously converted into fixed air, while the elastic part enters the vital fluid, communicating to it not only the red colour, but heat, and the principles of life and sensation, as will be more fully explained in the sequel. On these propositions, which constitute in a great measure the fundamental principles of the doctrine of _oxygenation_ of the human body, we may remark,