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body. As a consequence, if these arteries be fixed without suitable 

 preparation they present varying grades of contraction of the media, 

 and it is impossible with this variation to arrive at any sure con- 

 clusions regarding the relative development and thickness of intima 

 and media. To make a satisfactory comparison, it is essential to 

 bring all the arteries that it is desired to compare, to a common con- 

 dition. This is accomplished by destroying the contractihty of the 

 muscle fibres of the media by the use of some reagent such as a solution 

 of potassium sulphocyanide, or ammonia vapour, and when the arteries 

 are thus rendered thoroughly lax they are expanded under a pressure 

 not exceeding that to which they have subjected during life (I now 

 employ that of 100 mm. of mercury), and in this expanded state they are 

 subjected to fixation. It will be seen that by this means the arteries 

 become strictly comparable. 



But the method has other advantages. Owing to the fact that 

 the artery undergoes fixation in the expanded phase, the elements 

 of the middle coat are stretched evenly, so that the structure of this 

 coat can now be studied in a way that was wholly impossible under the 

 old more haphazard method. 



The prevalent teaching with regard to the middle coat of the 

 aorta, and of arteries in general, down to those of the very smallest 

 type, is that the muscle fibres are circularly disposed. 



But the method has other advantages. Owing to the fact that 

 the artery undergoes fixation in the expanded phase, the elements 

 of the middle coat are stretched evenly, so that the structure of this 

 coat can now be studied in a way that is wholly impossible under the 

 old more haphazard method. 



The prevalent teaching with regard to the middle coat of the 

 aorta, and of the arteries in general, down to tiiose of the very smallest 

 type, is that the muscle fibres are circularly disposed. 



It is true that Kölliker (2), Thoma, Jores, and others have laid 

 emphasis upon existence of muscle fibres on the inner side of the 

 internal elastic lamina, fibres which are special developed in the 

 subclavian artery, and that Goodall (3) in his studies upon the 

 regeneration of the uterine arteries has brought forward evidence to 

 show that muscular elements in the intima can be regenerated from 

 the media proper. But this " musculo-elastic layer" of Jores (4) is 

 so distinct and separate that, lying within the internal elastic lamina, 

 it is usually regarded as a portion of the intima. It is true also that 



