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traversing this tube for a certain distance, it is then made to pass 

 through another tube continuous with the first, but cooled to or below 

 zero, the velocity of the running fluid is diminished from that which 

 was maintained in the heated tube. The manner in which I have 

 sought to remedy this evil is the following : — The flat support, to which 

 is attached the essential part of the instrument, is made so as to contain 

 two moveable iron heaters ; when these are removed, and heated, and 

 then sent home into their respective cavities, the warmth they contain 

 is communicated first to the copper support, and thence to the glass tube? 

 through which the blood courses. 



The next objection refers rather to the mode of using the Hsemodro- 

 mometer than to the instrument itself. Yolkman's apparatus was, you 

 will remember, filled with water previously to operating. Now, no one 

 will refuse to recognise the inadvisability of the blood having to meet 

 a fluid of a very different specific gravity from itself, and one, more- 

 over, whose total immobility it has to overcome ere it can itself 

 move an inch. I look upon this as a most serious objection to Yolk- 

 man's mode of estimating the velocity of movement of fluid in a tube ; 

 and indeed Yolkman himself would seem to have anticipated that the 

 validity of his method would be called into question on this account, 

 since he takes care to inform us that the water is moved into the peri- 

 pheral arteries with but little admixture with the blood. I can only 

 say that I have put Yolkman's statement to the test of experiment, the 

 most reliable criterion, and I have invariably found the mixture of the 

 two fluids to be most considerable, and the specific gravity of the re- 

 sulting mixture to vary much from that of either the blood or water. 

 "When using my instrument, I apply one end of the tube to the cut end 

 of the artery whenee the blood flows, and I apply suction at the other 

 end, so as to create a vacuum, into which the flood flows freely. When 

 it has arrived at the opposite end, having turned the stopcock, I remove 

 the ligature which had been placed on the peripheral end of the artery, 

 and introduce the end of the tube into that of the vessel ; and the blood 

 flows, on again turning the stopcock, as though it experienced no in- 

 terruption whatsoever. Of course, these latter operations should be 

 performed as quickly as possible ; and, in order to avoid the trouble of 

 tying and untying ligatures, I make use of a minute forceps — one which 

 on pressing with the fingers opens, and on removing the pressure closes 

 with a tight grip. 



I have now mentioned the four great objections which I have to 

 Yolkman's Haemodromometer : each one of them tends to decrease the ve- 

 locity of the blood's movement ; and hence, when we consider the combined 

 effect of these, we must allow that the results of experiments made with 

 this instrument are not such as can be relied upon, nor do they correctly 

 estimate the velocity tvith which the blood moves in the arteries. 



It now behoves me to describe a Hsemodromometer which I would 

 propose as a substitute for Yolkman's ; and I must confess that I feel 

 considerable diffidence in so doing, not because I myself doubt for one 

 instant the superiority of my instrument as far as regards accuracy, but 



