38 CHEMICAL AND PHYSICAL METHODS 



This is what takes place for hormones amongst others. We 

 now understand the troubles brought about by lesions in 

 the thyroid gland. Any diminution in the secretion of the 

 hormone manufactured by this gland is followed by severe 

 accidents: cretinism, myxoedema, goitre. Physiology brought 

 us this far. Now, biological chemistry has not only succeeded 

 in purifying and obtaining in crystalline form the active 

 principle, thyroxin, which contains four atoms of iodine, but 

 has synthesized this compound artificially. The introduction 

 into the organism of two milligrams a day of thyroxin is 

 sufficient to dispel all morbid symptoms and often brings 

 about a complete recovery. The result is identical, whether 

 thyroxin extracted from organs or the synthetic product is 

 employed and, as these active substances are pure, a minimum 

 dose, which can be indefinitely tolerated, suffices. Chemistry 

 has solved the practical problem which was propounded by 

 medicine and studied by physiology. 



This is an example amongst twenty. Up till now, only 

 thyroxin and adrenalin have been synthesized. The other 

 hormones are extracted from organs of animals. But the 

 constant strides made in this direction permit us to look 

 forward to the day when they will be manufactured directly 

 from pure chemicals. In the same way insulin (hormone of 

 Langerhan's islets) renders the greatest services in serious 

 cases of diabetes. It is certain that the mechanism of the pro- 

 duction of thyroxin, insulin, and adrenalin in the glands 

 themselves escapes us altogether. But it does not matter, if 

 we have understood the part they play as regulators of certain 

 physiological functions in the organism. 



We know very well that vegetable cells chemically fix nitro- 

 gen at normal temperature, whereas we can only obtain the 

 same result, in vitro, around 500° C. But from a practical 

 point of view the important thing is to understand the role of 

 nitrogen in the metabolism of plants. The rest will perhaps 

 come later. 



It might be objected that the practical point of view should 

 not be considered in science. But much as we beheve that a 



