704 AisrisruAL report Smithsonian institution, 19 2 8 



grew out in about a third of the usual time. It can easily be under- 

 stood why this should be, for their bodies were receiving an ex- 

 cessive amount of thyroid principle, that manufactured by their 

 own thyroids plus that given to them by the experimenter. 



Thyroid function has been tested out on another close relative 

 of the frog family. In Mexican waters there is a strange creature 

 known as the axolotl. It is considered quite a delicacy by the 

 Mexicans, though I think that if you ever saw one its gastronomic 

 possibilities would not interest you. The axolotl is a sort of halfway 

 Jiouse along the evolutionary path, between a fish and a frog. It 

 looks like a huge tadpole, for it is several inches long, that had 

 started out to be a frog but thought better of it, and remained a 

 grotesque-looking object with gills, a finned tail, square head, and 

 short fore and hind limbs. This is the usual adult form of these 

 creatures; they breed in this form, many of them never developing 

 into land animals and a few others doing so very, very slowly. If 

 they are fed upon beef thyroid — even one or two meals is enough — 

 they develop into air-breathing animals. They lose their gills and 

 tail fin and develop air-breathing organs. The head becomes oval 

 and the eyes prominent. 



Here is an instance in which an animal, forsaken, as it were, at a 

 certain wayside station in the evolutionary journey, has been brought 

 a step further by an internal secretion. I promised not to speculate, 

 but I can not help but wonder just how important a part the ductless 

 glands have played in the evolutionary process. 



The thyroid has another entirely different duty to perform be- 

 sides those mentioned before. Its hormone is to the body as a 

 forced draft is to a furnace. It fans the fires of life. You all know 

 that the body shows a very real likeness to a furnace or an internal- 

 combustion engine. Its muscles consume fuel and in doing so use 

 oxygen and give out carbon dioxide, just as any combustion engine 

 does. Energy is liberated, heat is produced, and work is done. 

 Thyroid extract increases the combustion in the muscles. More 

 heat is produced with extract than without. The fire in each cell 

 burns more fiercely. The metabolism, as the physiologists say, is 

 increased. 



In those suffering from thyroid lack the fires are dampened down. 

 They glow dully, not brightly as they should ; metabolism is lowered. 

 The metabolism may be altered 50 per cent either way by an increase 

 or a decrease in thyroid secretion. On this account very serious 

 effects will result if a normal individual should take thyroid extract 

 for any length of time, for in that case the administered dose added 

 to the natural secretion would increase the combustion within the 

 body to a dangerous degree. Sometimes the thyroid has an exagger- 

 ated sense of what is required of it and manufactures more of its 



