THE RED CORPUSCLES. 27 



motion in the fluid is the biconcave discoid shape 

 of the red corpuscles ; for as they roll over it will be 

 seen that their outline is no longer circular as when 

 lying flat, but, on the contrary, a lateral view of the 

 disks is obtained, and the flattening and incurvation 

 of the surfaces become evident. 



When the motion in the layer of blood, in what- 

 ever way it may have been produced, is subsiding, it 

 will be seen that whenever one corpuscle comes in 

 contact with another the two seem to be in some 

 way attracted to one another, so as to adhere closely 

 by their opposed surfaces; and other corpuscles com- 

 ing in the same way in contact with these and adher- 

 ing, little piles or rouleaux are thus produced, which 

 form by their junction with one another a network, 

 extending throughout almost the whole of the pre- 

 paration. In the cords of this network nearly all 

 the red corpuscles are involved, and now for the 

 most part are seen edgeways; but in other parts of 

 the preparation where the layer of blood is very thin 

 the space being too small to allow the corpuscles 

 to stand edge up, and to combine so completely to 

 form rouleaux they may be found still lying flat 

 and distinct from one another; and these more iso- 

 lated corpuscles may now be subjected to careful 

 examination. Keeping a single red corpuscle in 

 view, if it be brought exactly into focus that is to 

 say, if the microscope be so adjusted that the con- 

 tour of the corpuscle is as distinct as possible it will 

 be observed, with the power (800 diameters) which 

 is at present being employed, that the middle part 

 appears slightly darker than the rim, whereas if, by 

 means of the flue adjustment, the objective be now 

 brought somewhat nearer (lower), the middle part 

 will come to appear lighter. 



The cause of this is probably to be found in the xhape 

 of the corpuscle, the middle part of which acts upon the 

 light like a very weak biconcave lens, refracting the rays 

 of light which nre transmitted through it slightly out- 



