798 THE THYROID BODY. [BOOK n. 



The thyroid body is very apt to become enlarged, sometimes 

 enormously so ; and is then spoken of as goitre. The enlargement 

 may be due simply to an increase in the number of otherwise 

 fairly normal alveoli and septa. But very often a number of 

 alveoli become more or less confluent, forming a cyst ; and at times 

 the whole gland appears to be composed of a number of cysts of 

 varying size, frequently loaded with ' colloid ' material. There is 

 also a form of goitre in which the enlargement is chiefly or even 

 exclusively due to an increase in the vascular supply, the blood 

 vessels being abnormally distended ; and this apparently may 

 occur without any structural changes in the walls of the blood 

 vessels. Sometimes however the arteries undergo aneurisrnal 

 enlargements, with changes in their coats. 



If the so-called colloid material be regarded as a nucleo-albumin 

 the thyroid may be said to yield hardly any other proteids. The 

 ' extractives ' appear to consist of kreatin or kreatinin in not in- 

 considerable quantities, xanthin, and lactic (paralactic) acid ; guanin 

 is said to be absent. In large and old cysts cholesterin is sometimes 

 present ; and when, as often happens, extravasations of blood into 

 the cysts have taken place, haemoglobin, or at a later stage 

 haamatoidin (bilirubin), has been found. 



495. The large supply of blood to the thyroid and the 

 presence of the extractives just mentioned suggest the idea that 

 the organ is the seat of some of the subsidiary metabolic processes 

 to which we referred in the last section. And we now possess 

 conclusive experimental and other evidence that the organ exer- 

 cises a remarkable influence on the nutrition of the body. 



When in certain animals (monkeys, dogs and other carnivora, 

 and the same has been observed in man) the gland is completely 

 extirpated, the removal is followed by symptoms which at first 

 are specially connected with the central nervous- system, but 

 subsequently take on the form of disordered nutrition (cachexia as 

 it is called) of the body at large. The earlier symptoms are 

 muscular twitchings, tremors, spasms and even convulsions, all 

 indicating an abnormal excitation of the central nervous system ; 

 these are followed by a lessening or even loss (paralysis) of 

 voluntary movements and also of sensation, bringing about a 

 characteristic apathy or lethargy ; and histological changes in the 

 central nervous system, probably acting as causes of the above 

 symptoms, have been observed. The respiration is troubled, and 

 cardiac disorders as well as difficulties in swallowing are at times 

 met with ; these are probably due in part at least to disorder 

 of the spinal bulb. The general nutritional disorders affect 

 specially the skin and the connective tissue ; at times an excess 

 of mucin appears to be present in the latter, but this is by no 

 means constant and its importance has probably been exaggerated ; 

 the other tissues suffer as well and the whole body becomes 

 emaciated. The temperature of the body falls below the normal, 



