ZOOLOGY AND BOTANY, MIOKOSCOPY, ETC, 677 



The modification illustrated by Fig. 159 was employed to prove 

 that the pressure applied to the tissue in the centre of the compressed 

 area is really that which is signified by the manometer. The little 

 round chamber A, closed above by the glass plate B, and on the under 

 end of which a membrane is fastened, is held by an appropriate 

 holder immediately above the web, but not in contact with it. The 



Fig. 159, 



ordinary glass slide E, upon which the web G rests, serves to exert a 

 coimter-pressure. In order to prevent the membrane bulging out 

 laterally, there is placed round the lower part of the cylinder, but not 

 connected with it, a light ring of waxed paper, seen in section at D. 

 The paper ring rests upon the web, and is so light that its presence 

 has no appreciable influence on the circulation of the part. 



In so far as the pressure is concerned, the authors have, with this 

 arrangement, included a portion of web within a rigid box, closed 

 below by the glass slide lying on the microscope-stage, above by the 

 little glass plate B, and limited laterally by the cylinder and the ring 

 of waxed paper, and the membrane. There is, at the same time, no 

 interference with the entrance and exit of blood to and from the part 

 of the web to be examined, other than that intentionally produced by 

 raising the pressure within the chamber. 



They made a number of careful experiments with this little 

 apparatus, comparing the results obtained by its help, with those given 

 by the simpler arrangement illustrated by Fig. 156, and are thoroughly 

 convinced that, for any individual case, cceteris paribus, the arterioles 

 and capillaries of a given part are made to collapse at the same pres- 

 sure with both methods. It is not pretended, of course, that, with 

 the arrangement represented in Fig. 156, the pressure on the web is equal 

 over the whole area of contact between it and the membrane. Doubt- 

 less, at the edge of this area, the pressure applied will be somewhat 

 less than it is at the centre. It is only the central part, however, 

 which can come within the field, and for this part, as already men- 

 tioned, the pressure which acts upon the tissue is correctly indicated 

 by the manometer. 



The frogs used (B. esc. as well as B. temp., and the greater 

 number winter frogs) were for the most part uncurarized, as the blood- 

 pressure of curarized animals is liable to variations which do not 

 occur in the case of uncurarized animals. It was found that it is very 

 easy so to fasten a frog upon an appropriate holder, that, while the 



