798 THE ENDOCRINE ORGANS, OR DUCTLESS GLANDS 



can be produced experimentally by the removal of the gland in animals. 

 By observations on the effect of administration of thyroid extract to 

 cretinous or myxedematous patients, prompt amelioration of the symp- 

 toms occurs, which certainly suggests that the real cause is the absence 

 of an internal secretion. There is probably nothing more striking in 

 the whole domain of therapeutics than this effect from the administration 

 of thyroid extract or, more so still, of thyroxin. If the treatment is 

 started early enough, the cretinous child from being an ill-developed 

 idiot quickly catches up with children of his own age and becomes in 

 every respect normal. Even if this treatment is not undertaken until 

 the child is several years of age, it is remarkable how quickly the benefit 

 may show itself. In myxedema and cachexia strumipriva also, the 

 symptoms very quickly disappear and the person becomes perfectly nor- 

 mal by the treatment. In all these conditions, however, the thyroid 

 extract must be administered continuously in order to prevent the reap- 

 pearance of symptoms. 



Quite distinct from the above described conditions of hypothyroidism 

 are those produced by an excess of thyroid autacoid in the blood, namely, 

 hyperthyroidism. Such a condition can be produced experimentally in 

 normal animals by the administration of thyroid extract or of thyroxin 

 (Kendall). In man its continuous administration is soon followed by great 

 quickening of the pulse with some irregularity, flushing of the skin, in- 

 creased perspiration, tremor in the limbs, emaciation, and marked nervous 

 excitability. Along with these symptoms, metabolic investigations have 

 shown that the energy output per square meter of surface is greatly in- 

 creased, being sometimes nearly doubled ; that the nitrogen excretion is ex- 

 cessive; and that alimentary glycosuria is very commonly present. The 

 body temperature is not, however, as a rule increased, because although 

 metabolism is excited, yet heat loss is correspondingly increased. Ex- 

 ophthalmos is said to develop very occasionally after such administra- 

 tion, but this is doubtful. Lastly, there are usually digestive disturb- 

 ances, although the appetite is likely to be increased. The pulse is quick- 

 ened after administration of thyroxin only when protein food is also taken. 

 This is believed by Kendall to be due to the association between the thyroid 

 hormone and the metabolism of the amino acids.\It has been shown that 

 a single large dose of thyroxin has little demonstrable effect, whereas 

 minute doses administered over a prolonged period produce decided, toxic 

 manifestations, and, if the administration is persisted in, death results^- 

 These facts are explained on the hypothesis that thyroxin acts in the body 

 as a catalyst and hastens certain metabolic processes which are responsi- 

 ble for the symptoms, and that they are not due to the action of thyroxin 

 perse. (Kendall.) 42 



The symptoms following the injection of the extract are very similar 



