BAIRD &TATLOCK (LONDON) LTD. 



871 T Clinical Viscometer, for taking viscosity of blood. Full particulars as to use sent with 

 each instrument. Price tube only (see page 179 for illustration) 



036 



Extras : 

 872 T Price per set of 6 tubes, marked with time value in case 



873 T Stop Watch 



1 2 6. 

 1 I 



874 T One complete set consisting of 6 capillary tubes, each tube marked with the time value for 

 water ; stop-watch (which is started, stopped, and restored to zero by pressure of the 

 finger) ; bottle containing 6 Wright's lancets ; metal holder and heater for the tubes ; small 

 force pump, rubber tubing, and clearing wires ; table for readily finding blood viscosities 

 relative to water 



2 10 



Fig. i. Determination of the area of the blind-spot 

 arranged for use with the right eye. 



875 



Fig. 2. Showing the reverse side of the instrument. 

 875 



875 T The Colour Blind Margin of the Blind-spot, and the Scotometer, by John Berry 

 Haycraft, M.D., D.Sc., Professor of Physiology, University College, Cardiff . . 



5 5 



The observer rests his chin on one of the curved surfaces (2) which may be raised or lowered by the screw 

 (3) ; his left eye being closed he looks with his right eye through the metal ellipse (i) at the white mark on the 

 black metal plate. The white head of the nail, which is placed in the metal hole to the right of mark is then 

 in the blind-spot and is invisible. 



By means of the screw (4) the nail head can be raised or lowered. The screw is turned until the nail head 

 becomes visible. As soon as it is visible the nail head is pressed, and this records its position in the way to 

 be described presently. Thus the length of the blind-spot in a vertical direction is recorded. 



The screw (5) is then loosened. When this is done turning screw (4) produces a horizontal movement of 

 the nail head. The screw (4) is then turned each way until the nail head becomes visible, and the length of 

 the blind-spot in a horizontal direction is registered. 



The extent of the blind-spot in other vertical or horizontal directions can be registered in a similar manner, 

 and the area of the blind-spot marked out. 



In making observations with the left eye the plate is rotated so that it projects on the left side of the 

 instrument. 



The recording of the position of the nail head is effected as follows : 



A transfer paper (A), and a paper ruled in square millimetres (B), are placed in the flat box, which is closed 

 by the door (D). The point of the nail projects from the centre of the tube (c), so that when the nail head is 

 pressed it marks a dot upon the ruled paper. A line joining the dots obtained in the manner given in the 

 preceding paragraphs gives the area of the blind-spot. The blind-spot may, with this instrument, not only be 

 mapped out accurately, but the larger blood-vessels entering, and leaving it, may also be noted, and mapped 

 out for a short distance in their course. 



CROSS STREET HATTON GARDEN, E-C- 



180 



