SECRETION. 207 



tially or completely by grafting a portion of the pancreas elsewhere in the 

 abdominal cavity or even under the skin. The duets of the gland may be 

 completely occluded by ligature or by injection of paraffin without causing 

 a condition of permanent glycosuria. 



The condition of glycosuria produced by removal of the pancreas is desig- 

 nated frequently as pancreatic diabetes and offers many analogies to the similar 

 pathological condition in man known as diabetes mellitus. The cause of the 

 glycosuria is obscure. It has been shown that in severe cases sugar appears 

 in the urine even when the animal is deprived of food, although the quantity 

 is increased by feeding and especially by carbohydrate food. Examination 

 of the blood shows that the percentage of sugar in it is increased above the 

 normal, from 0.15 per cent, to 0.3 or 0.5 per cent. In the liver, on the con- 

 trary, the supply of glycogen disappears. Carbohydrate foods when fed cause 

 no deposition of glycogen in the liver, and apparently escape consumption in 

 the body, being eliminated in the urine. It is said, however, that one form 

 of sugar, levulose, offers an exception to this general rule, since it causes a 

 formation of liver glycogen and seemingly is consumed in the body. 



We may believe from these experiments that the pancreas produces a 

 substance of some kind that is given off to the blood or lymph, and is 

 either necessary for the normal consumption of sugar in the body, or else, as 

 is held by some, 1 normally restrains the output of sugar from the liver and 

 other sugar-producing tissues of the body. What this material is and how it 

 acts has not yet been determined satisfactorily. The most plausible theory 

 suggested is that the internal secretion produced contains a special enzyme, 

 glycolytic enzyme (Lepine), whose presence in the blood is necessary for the 

 consumption of the sugar. Such an enzyme may be obtained from blood 

 (p. 354), but it is not proved whether it is a normal constituent or whether it 

 is produced after the blood is shed by the disintegration of some of its cor- 

 puscular elements. This theory therefore cannot be considered as more than 

 a possibility. It is interesting and suggestive to state in this connection that 

 post-mortem examination in cases of diabetes mellitus in the human being has 

 shown that this disease is associated in some instances with obvious alterations 

 in the structure of the pancreas. 



The Thyroid Body. — The thyroids are glandular structures found in 

 all the vertebrates. In the mammalia they lie on either side of the trachea 

 at its junction with the larynx. In man they are united across the front oi 

 the trachea by a narrow band or isthmus, and hence are sometimes spoken 

 of as one structure, the thyroid body. In some of the lower mammals 

 (e. g. dog) the isthmus is often absent, The thyroids in man are small 

 bodies measuring about 50 millimeters in length by 30 millimeters in width ; 

 they have a distinct glandular structure but possess no ducts. Histological 

 examination shows that they are composed of a number of closed vesicles vary- 

 ing in size. Each vesicle is lined by a single layer of cuboidal epithelium, 

 while its interior is filled by a homogeneous glairy liquid, tin' colloid substance 

 1 See Kaufmann: Archives de Physiologie normah ft pathologique, 1895, p. 210. 



