The Microscope. 267 



will float around freely, on their edge. It is soon noticed, this 

 writer says, that the corks will come together in rows, with 

 their concave sides together just as we now see the so-called 

 rouleaux of human blood. Another writer says that on the 

 outside of the red corpuscles there is a glutinous substance and 

 that this holds the corpuscles together in rows, and they assume 

 this particular arrangement because thej' - take up less room 

 that way. It certainly must be true that this glutinous sub- 

 stance alluded to does not exist during the circulation of the 

 blood, for it is a well known fact that the red corpuscles flow 

 freely in the centre of the stream in the blood vessels, while 

 the white ones flow much more slowly, clinging to the walls of 

 the vessels as if they indeed were somewhat glutinous in their 

 nature. 



2. Their Shape. — After noticing the rouleaux, a slight tap 

 on the edge of the cover glass will separate the corpuscles and 

 they can now be studied to advantage. The shape of the red 

 corpuscle is seen to be circular, and, watching some as they 

 float about turning frequently on their edge, biconcave with 

 rounded edges. 



3. Their " optical delusions." — The corpuscles act with 

 reference to the light as biconcave lenses, hence when the ob- 

 jective is slightly within the focus, the centre of each corpuscle 

 appears light, and when slightly without the focus the center 

 appears dark. This led the old observers to regard the centre 

 as a nucleus. They were, we say, " optically deluded." The 

 shape is readily altered by various reagents to be mentioned 

 later. 



4. Their Color. — When seen in mass, or in a number of 

 layers under the microscope they present a reddish color ; but 

 when seen alone, or in a single layer, they are of a yellowish- 

 green color. 



5. Their Structure. — They appear to have no enveloping 

 membrane, only the outer part of the corpuscle seems more 

 dense than the inner part. No nucleus is visible without the 

 use of reagents, and none is visible with the use of any ordinary 

 reagent. For a discussion of this question our readers are re- 

 ferred to our large manual. 



