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The first objection which I have to state to Yolkman's Hsemodro- 

 mometer is applicable to mine also — it is that of the sudden propulsion 

 of the blood from a tube of 'elastic and contractile force into one perfectly 

 inelastic, and one not having muscular force. The effect of this condition 

 is more serious than is generally imagined ; for when the natural calibre 

 of the artery, or its caliber when not in the distended state, corresponds 

 with that of the glass tube, the former is capable of receiving a greater 

 quantity of blood than the latter ; and the contractility called into 

 action by this expansion is now exerted, and contributes to quicken the 

 velocity of the remaining fluid. ]STo such conditions as these exist in the 

 glass tubing ; and the only plan I have adopted, with a view to lessen 

 this difference between the two tubes, is to use a glass tube whose ca- 

 liber will be equal to that of the artery when at a moderate expansion. 



The second objection is one which, although I have considerably 

 lightened, I have not been able entirely to meet, namely, the existence 

 of sharp turns in the long glass index tube. In Yolkman's instrument there 

 are three of these sharp turns ; one at the entrance, and another at the 

 exit, both of which are right-angled ; the third is situated in the centre 

 of the tube, and is in reality made up of two turns, each of which is right- 

 angled also ; the effect is alleviated in the latter case by the curves being 

 well directed ; but in the former cases, namely, at entrance and exit, the 

 arrangement is directly angular. I need not say how detrimental to the 

 velocity of a running fluid the presence of these angles is, nor need I 

 explain how the column of blood which is being propelled into the 

 tube, meeting at its entrance an opposing wall has to be reflected, as it 

 were, from it before it pursues its course. The same takes place at the 

 exit of the tube, except that here the reflection, if I may be allowed 

 the term, takes place in an opposite direction ; so that, instead of the 

 fluid being prevented to a degree from entering the tube, it is here hin- 

 dered in leaving it — not altogether, of course, but in a degree to affect 

 considerably the velocity of the movement of the contained fluid. At 

 the centre of the tube, also, is a sharp turn, arranged so that the fluid 

 arriving by one limb of the tube has to be sent back immediately after 

 moving round this sharp double turn in the opposite direction. My 

 instrument must be regarded as of much better design in respect to 

 curves in the tube than that of Yolkman ; for, while the fluid entering 

 into his is immediately sent in a direction at right angles to the course, 

 the direct course of mine is interrupted but very little. The curves in 

 my Hsemodrometer are greatly exaggerated, and the caliber of the tube 

 where they exist is slightly increased. 



The third objection which I would urge is the sudden propulsion of 

 hot blood from a vessel of a certain temperature into another of a much 

 lower degree of heat, or almost cold. This defect would seem to be of 

 such trivial consequence as to warrant its being entirely overlooked. 

 The experiments which I have made touching this question, however, 

 induce me to insist on the above as a decided objection. I have seen 

 that when blood or any other fluid is heated to a certain point, and 

 is passed through a vessel of a certain temperature, and when, after 



