294 NON-NITROGENOUS NEUTRAL BODIES. 



the function of the pneumogastric nerves ; for when they have 

 been divided he has also found sugar. 



Uses. Since glucose, which, as we have already seen, is 

 principally formed in the intestinal canal from the starch of the 

 vegetable food, appears, from the results of all physiological enqui- 

 ries, to be a true element of nutrition, (see "Nutrition,") the 

 question that remains to be considered is how it is applied, or 

 what is its use in the animal organism ? It belongs, according to 

 Liebig, to the food for the respiration ; and if we regard it purely 

 in this light, its object is easily understood ; it undergoes a process 

 of combustion by combining with the inspired oxygen, its final 

 products being water and carbonic acid, and tends to support the 

 animal heat, if we regard this as an independent process. If, 

 however, we entirely concur in this view, we have still to enquire 

 whether the sugar does not previously undergo other changes and 

 serve other objects, before it yields carbonic acid and water as the 

 final products of its combustion. 



It must excite our surprise that in diabetes, where, in refer- 

 ence to the respiration, the saccharine and amylaceous elements of 

 food appear to be entirely lost, the respiration and the animal heat 

 are so well supported ; for although pulmonary tuberculosis is a 

 frequent complication of diabetes, this is by no means invariably 

 the case; and it may occur without any affection of the lungs. It 

 certainly seems very remarkable that such a mass of the respira- 

 tory food can be lost without inducing any symptom of a dis- 

 turbed respiration or of a diminished animal heat. 



We have already referred (p. 257) to the hypothesis of the 

 conversion of sugar in the intestinal canal into/iz/, and shown that 

 it is unsupported by facts ; but we do not deny that in some part 

 of the animal body (at least under certain relations) sugar may be 

 metamorphosed into fat. Moreover, we are still so ignorant 

 regarding the different changes which the sugar undergoes in the 

 blood, that, to a certain degree, we must content ourselves with 

 the consideration of questions that may lead us on the true path 

 of inquiry. We have already pointed out the probability that 

 the lactic acid occurring in the animal body is formed from sugar 

 (p. 101) ; under special relations butyric acid may also be produced 

 from it (p. 59). The alkalescence of the urine observed by Ber- 

 nard after the injection of glucose would almost seem to indi- 

 cate that the sugar in the blood is converted into an acid, which, 

 combining with the alkali of the blood, yields carbonated alkali as 



