METHODS OF INVESTIGATION 21 



knowledge of the thyroid apparatus. The same may be said 

 of the pituitary body and acromegaly, and doubtful as may 

 be the connection between enlarged thymus and sudden death 

 in infants, yet this is almost the only allegation which points 

 to the organ having any definite function. 



Experimental pathology in the form of extirpation experi- 

 ments has been largely employed in the attempt to elucidate 

 the functions of the glands with an internal secretion. The 

 method has undoubtedly brought to light many important 

 new facts. It has revealed, for example, the fact that certain 

 of these glands, such as the adrenal and the pituitary, are 

 essential for life, and that removal of the thyroid apparatus 

 entails in most animals very serious results. It has taught 

 us, further, that extirpation of the thymus is without obvious 

 effects. But the results obtained by different observers have 

 often been very contradictory, and the method of complete 

 extirpation has several drawbacks. In the first place the 

 technical difficulties are always very considerable, and are 

 often wellnigh insurmountable. This applies especially to the 

 pituitary body, though modern surgical skill seems at last to 

 have triumphed (see p. 361). It is very frequently impossible 

 to remove just the organ one wishes to remove without doing 

 considerable damage to other tissues. Thus the extirpation 

 of the adrenal bodies and the thyroids must always involve 

 considerable injury to nervous structures and bloodvessels. 

 This consideration must largely account for the contradictory 

 results obtained by different observers. The difficulty of 

 removing the parathyroids without considerable injury to 

 the thyroids can scarcely be overcome, and the successful 

 removal of the pituitary cannot have been performed by more 

 than a very few observers. 



Again, we must remember that complete removal of an 

 organ, even if successful from a surgical standpoint, is, owing 

 to its suddenness, an event which can never happen in nature, 

 and can never happen in pathology, and we must be cautious 

 in interpreting the results. The method, however, under 

 modern surgical conditions, is capable of fruitful results, for 

 animals do not appear to suffer to any considerable degree 

 from surgical shock. 



Extirpation experiments performed in a series of steps at 

 successive operations are more valuable than when the whole 



