CH. XXIII.] THE PARATHYROIDS 337 



subcutaneous tissues, which in time is replaced by fat ; the hair falls 

 off, the hands become spade-like; the whole body is unwieldy and 

 clumsy like the mind. 



A similar condition occurs after the thyroid is completely removed 

 surgically ; this is called cachexia strumipriva ; this operation, which 

 was performed previous to our knowledge of the importance of the 

 thyroid, is not regarded as justifiable nowadays. 



Lastly, in many animals rejaoval of the thyroid produces analogous 

 symptoms, in the overgrowth of the connective-tissues especially 

 under the skin, and in the nervous symptoms (twitchings, convul- 

 sions, etc.). 



The term Myxcedema was originally given under the erroneous 

 idea that the swelling of the body is due to mucin. In the early 

 stages of the disease there is a slight increase of mucin, because 

 all new connective-tissues contain a relatively large amount of ground 

 substance, the most abundant constituent of which, next to water, 

 is mucin. But there is nothing characteristic about that. 



The discovery of the relationships between the thyroid and these 

 morbid conditions is especially interesting, because important practical 

 results in their treatment have followed close on the heels of experi- 

 mental investigation. The missing internal secretion of the thyroid 

 may be replaced in these animals and patients by grafting the thyroid 

 of another animal into the abdomen; or more simply by injecting 

 thyroid extract subcutaneously ; or even by feeding on the thyroid 

 of other animals. This treatment, which has to be kept up for the 

 rest of the patient's life, is entirely successful. Chemical physiologists 

 have been diligently searching to try and discover what the active 

 material in thyroid extract is which produces such marvellous results ; 

 the view at present held is that the efficacy of thyroid extract is due 

 to a substance which Baumann separated from the gland, and which 

 stands almost unique among physiological compounds by containing 

 a large percentage of iodine in its molecule. TJiyro-iodin or lodo- 

 thyrin, as this substance has been called, is present in combination 

 with proteid matter in the colloid substance. 



Intravenous injection of thyroid extract in a normal animal 

 lowers blood-pressure ; but in an animal from which the thyroid has 

 been removed it stimulates the heart and raises blood-pressure. 



Parathyroids . 



These are small bodies, usually four in number, situated in the 

 neighbourhood of, or embedded in the substance of, the thyroid. They 

 are made up of elongated groups of polyhedral cells, bound together 

 by connective- tissue and well supplied with blood-vessels. Some 

 observers look upon these as being even more essential to healthy 

 life than the thyroid, but this point is by no means decided. 



Y 



