318 



is rather difficult of description. The handle commands the course of 

 the tube by means of two cogged wheels, so that when it is turned in 

 one direction it allows a free joassage directly from one end to the 

 other ; and when it is turned in the opposite direction this free passage 

 is interrupted, and another passage, namely, from one end, along 

 the hairpin tube, to the other end is opened ; so that at the will of the 

 operator he can open one communication to the exclusion of the other, 

 but he cannot obtain a double communication. The glass hairpin - 

 shaped tube is attached to a board, on which is fixed a scale. 



"When the Hsemodromometer is used, alarge artery is exposedfor about 

 three inches, and a piece is cut out of it after means have been adopted 

 for the prevention of hemorrhage. The next step is to fix the cone- 

 shaped open cups into the open ends of the artery, and each end of the 

 horizontal metal tube is then fitted into its corresponding cup. I should 

 mention a precaution which it is here' necessary to observe — it is this : 

 to so arrange the distance of the cups that, when the horizontal tube 

 is introduced between them, the continuation of the vessels is as little 

 altered as possible by the intervening mechanism. The blood now con- 

 tinues to circulate through the horizontal tube as it would were the 

 vessel entire, the stopcock being so turned as to shut off communication 

 with the glass tube. This* latter is now filled with water, and is fixed to 

 the horizontal tube by means of pipes. The arrangement is now com- 

 plete, and the stopcock is turned, so as to shut off the direct communi- 

 cation between the two ends of the horizontal tube. The blood now 

 enters the glass tube, and pushes the water before it into the peripheral 

 bloodvessels, with (according to Yolkman) only a very slight admixture 

 between the two fluids. 



I have now described at length this very ingenious instrument ; and it 

 would seem at first that it supplies what is needful, in every respect, and 

 that the results obtainable from experiments with it are very reliable. 

 On mature consideration, however, no one will fail to perceive that 

 there are grave objections to it; and it now devolves upon me to 

 mention those which have struck me as being most prominent. 

 There are one or two of these objections which I myself have not 

 succeeded in obviating ; and many will say that it were well that 

 I should pass over these, and confine myself to such as I can re- 

 move. Were I to heed such suggestions, I should not be performing 

 the duty I have taken on myself ; for, although the instrument which I 

 am about to describe I believe to have many advantages over that of 

 my brother physiologist, no one is more sensible of the fact than I am 

 that it is by no means a perfect instrument, and that it is itself open to 

 great objections — objections which I do not despair of being able to 

 remove at some future period, or which, I myself being incompetent, 

 will I doubt not be done away with, and that right speedily, through 

 the exertions of the learned physicists and physiologists to whose no- 

 tice I submit them. Thus, in mentioning objections to Yolkman's Hse- 

 modromometer which baffle my own inventive faculties to remove, I 

 anticipate the defects of my own instrument. 



