110 PRINCIPLES OF VETERINARY SCIENCE 



brought out very clearly the r61e played by the inorganic salts 

 in the ration. When cows were allowed a suitable salt mixture 

 in their ration of corn, grain and wheat straw, they maintained 

 a good state of nutrition and were able to produce vigorous calves. 

 Later the same cows were fed on the same rations minus the salt 

 mixture and while they were able to subsist themselves, they were 

 unable to reproduce living offspring. 



From the above facts it is clear that the following factors 

 are necessary to make a ration adequate for nourishment: a 

 sufficient amount of energy or fuel food; protein of poor, 

 medium, or good quality; a suitable inorganie content; an 

 adequate supply of the two as yet unidentified chemical sub- 

 stances belonging to the class of materials now called vitamines. 



THE DUCTLESS GLANDS AND THEIR FUNCTIONS 



The principal glands without ducts are the spleen, the thyroid, 

 the thymus, the adrenals, and the pituitary and pineal bodies. 

 They do not belong to the digestive system any more than 

 to any other one system, but are described here for conveni- 

 ence. Although situated widely apart in the body and having 

 no visible connection, they are dependent on each other. Little 

 is known about the functions of these glands. In recent years 

 it has been found that they play important r61es in the elabora- 

 tion of the so-called internal secretions, which pass directly into 

 the veins or lymphatics instead of being conveyed away by ducts. 

 The active principles or hormones of their secretions act in a 

 chemical manner to maintain what has been termed "the internal 

 secretory balance." That they are necessary is shown by the 

 fact that in most cases serious results follow their removal or 

 disease. They regulate and correlate some of the most impor- 

 tant physiologic functions of the body. 



The spleen is the largest ductless gland. It is very vascular 

 and is situated in the left portion of the abdominal cavity. In 

 the horse it is sickle shaped, weighs a little more than 2 pounds, 

 and averages 20 inches in length. It is bluish-red in color, and 

 is soft but not friable in the natural state. The function of the 

 spleen is not positively known, but it is supposed to have some- 

 thing to do with the formation and destruction of the red blood- 

 corpuscles which are found in the organ in great numbers. Its 



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