INTERNAL SECRETIONS 361 



also from the fact that the motor cortical fields soon become fatigued by elec- 

 trical stimulation, until in the later stages of the disease, when the voluntary 

 movements become extremely slow and imperfect, stimulation produces no vis- 

 ible effect at all. The same is true also with stimulation of the corona radiata 

 and of the spinal cord. At the height of the convulsions, on the contrary, the 

 excitability of the entire nervous system is plainly increased. 



Again, all those parts of the brain which are active in the psychical func- 

 tions become functionally reduced by extirpation of the thyroid. In myxoadema- 

 tous patients we meet with weak memory, extreme irritability, stupidity, etc., 

 which in turn find expression in a decline of muscular tone and in the vigor of 

 the bodily movements generally. 



Finally, disturbances in the temperature and the heat regulation of the 

 body are seen. A considerable rise in temperature has very often been observed 

 during the height of the muscular convulsion ; but when this stage has passed 

 a decided fall ensues in the monkey to 33. In man also the subnormal tem- 

 perature is one of the most constant symptoms, and the patient feels cold. 



In the growing organism after suppression of the thyroid, the bones fall 

 considerably behind in their development and the ossification of the epiphysial 

 cartilages and synchondroses is delayed materially. The psychical disturbances 

 are probably more pronounced also than in grown persons (Fig. 138). 



Most of these disorders gradually disappear after treatment with prepara- 

 tions of thyroid. The skin acquires again a normal appearance (Fig. 137, B) ; 

 metabolism increases in the above-mentioned case, reported by Andersson, after 

 nine months' treatment it had returned to the normal value of 2,099 Cal. = 32.3 

 Cal. per kilogram of body weight ; the utilization of foodstuffs is more complete ; 

 the muscular and nervous disorders are reduced, and in young individuals one 

 can often observe with this treatment absolutely brilliant results (Fig. 138, B). 



From all this it follows that the thyroid gland must be regarded as an 

 organ which, by internal secretion of certain substances, performs a vitally 

 important function. These substances represent either important constituents 

 of the liquids of the body, or are used for the neutralization of poisons which 

 may be present. We cannot say definitely whether the thyroid has still other 

 functions or not. 



From histological investigations of the process of secretion in the thyroid, 

 we appear to be justified in the assumption that the follicular contents are 

 elaborated by the epithelium surrounding the follicle ; and that it passes through 

 openings in the wall of the follicle formed by simple atrophy (colloidal fusion) 

 of the epithelial cells from the cavity of the follicle into the lymph spaces of 

 the gland. In the lymph spaces the contents are gradually diluted with lymph; 

 the secretion soon loses its characteristic consistency and ability to take stains, 

 and is added to the general circulation through the lymph vessels (Hiirthle). 



Our knowledge of the innervation of the thyroid is still very imperfect. 

 According to Exner, Jr., after section of the thyroid nerves of the cat on 

 one side, when the opposite half of the gland has been removed, various dis- 

 turbances (hyperaBsthesia, apathy, convulsive twitchings, etc.) appear during the 

 first few days, but disappear completely within a few weeks. How far these 

 disturbances are the direct result of the loss of nervous control, or whether they 

 are due to other circumstances, can scarcely be decided at present. Hiirthle 

 and Katzenstein were unable to produce any histological changes by stimulation 

 of the thyroid nerves. The latter succeeded, however, in demonstrating distinct 

 signs of degeneration in the thyroid of the dog after section of its nerves. 



