672 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



the control of the nervous system, and the path of this influence, which 

 originates in the neighborhood of the vaso-motor centre, ma}- be traced 

 along the spinal cord, and then, by means of the vagi, to the third and 

 fourth dorsal ganglia, from this to the thoracic ganglia, and from there 

 to the liver by some path not yet absolutely determined. 



The production of diabetes by such an operation is probably to be 

 regarded as of a vaso-motor nature. It seems clear that through this 

 operation the small branches of the hepatic artery are largely dilated, and 

 the liver, consequently, receives a larger amount of arterial blood, and 

 that simple division of any part of this nervous path, such, for example, 

 as removal of the first thoracic ganglion, will likewise produce diabetes. 



If the splanchnic nerves be divided previous to this operation gly- 

 cosuria will not result, evidently by withdrawing a large quantity of 

 blood into the abdominal organs and so preventing relatively anj* dilata- 

 tion of the hepatic artery. 



IV. THE STATISTICS OF NUTRITION. 



The preceding sketch as to the fate of the different organic food- 

 constituents gives but an imperfect idea as to the metabolic processes 

 occurring within the animal body. By a close comparison of the income 

 and outgo of the economy statistics of nutrition may be formed which 

 are of great value for obtaining an idea of the nutritive processes of the 

 economy under different forms of diet, and thus assist in the formation 

 of scientific methods of feeding. 



When we compare the income with the outgo, the ingesta with the 

 excreta, we learn not only what part of the ingesta is retained in the 

 body, but by the detection of substances in the excreta not present in 

 the food we may extend our idea of the changes which the body has 

 undergone under the influence of the food. 



In determining the true income of the body the constituents of the 

 faeces must be subtracted, for, as already noted, the faeces consist almost 

 solely of food-stuffs which have escaped digestion and absorption, the 

 amount of excretory matter in the faeces being so small as to be dis- 

 regarded. From the study of the composition of the food we know 

 that in certain amounts of proteids, fats, carbohydrates, salts, water, and 

 inspired air, the animal body takes in definite quantities of nitrogen, 

 oxygen, carbon, hydrogen, sulphur, phosphorus, salts, and water. 



The determination of statistics of nutrition is based upon the 

 following facts: — 



1. With the exception of wool- and milk-producing animals, all the 

 nitrogen is excreted in the urine ; that found in the faeces ma}' he 

 regarded as derived almost solely from undigested food. 



2. From the difference between the amounts of nitrogen in the food 



