THE CKETmiC DEGENERATION 449 



members of a given race in a given country will be found to be due to 

 other causes. 



Occupation. Manual laborers, particularly those exposed directly to 

 soil and water contamination, are particularly prone to the disease. Mac- 

 kenzie found 98 per cent of the endemic goiters of Lanarkshire among the 

 laborers and miners. In a rural community the clerks and other indoor 

 workers escape to a greater degree than do the agricultural classes even 

 when no difference of hygiene and general environment exists. 



Acute and Chronic Diseases. Among such may be mentioned acute 

 and chronic infections and intoxications, some of which may have been 

 demonstrated to cause petechial and sclerotic lesions in the thyroid gland. 

 It is, however, difficult to estimate accurately the amount of damage done 

 by such agents. The specific action of infectious diseases would be to 

 injure and diminish the amount of functionating thyroid parenchyma, thus 

 predisposing to the hypertrophic influence of the specific causes of cretinic 

 degeneration. As the gastro-intestinal tract has been demonstrated by 

 McCarrison to be a portal of entry of the toxic agents producing goiter 

 and cretinism (see below) more exact future observations may demonstrate 

 the role of chronic inflammations of the digestive canal such as catarrhal 

 colitis, as predisposing etiologic factors. 



The Influence of the Seasons bears a relation to the variation in the 

 iodin content of the thyroid, lowest, according to Seidell and Fenger's (6) 

 researches, during the first four months of the year. It is then that goiters 

 reach their maximal size by a process of compensatory hypertrophy. Out- 

 breaks of "Spring" or "Summer" goiter are not uncommon among new- 

 comers in European endemic centers. They may be possibly due to con- 

 tamination of the water supply by the spring rains or to a low spring and 

 summer iodin content of the affected thyroids. In animals seasonal varia- 

 tion in goiters has been traced to the low iodin content of food at certain 

 seasons. In countries of dry and rainy seasons the disease is more preva- 

 lent during the wet period owing to contamination of the water supply by 

 surface water. 



Other Predisposing Conditions. The thyroid gland is probably the 

 most important regulator of metabolic processes. Any factor which influ- 

 ences deleteriously the general metabolism or its nervous control will of 

 itself bring on added strain on this endocrin organ. Such are insufficient 

 food, air, space, residence in high altitudes (insufficient oxygenation), 

 great nervous and emotional strain, oversexual activity, gestation, etc. 



The Relation of the Thyroid Gland to the Cretinic Degeneration. 

 Two theories as to the relation of the thyroid gland to the cretinic de- 

 generation have been evolved. One viewpoint would recognize cretinic 

 degeneration merely as an endemic expression of hypothyroidism (Kocher, 

 V. Wagner, Combe, v. Jauregg, v. Eiselsberg, Hertoghe, Bayon, McCar- 



