224 RED PARTICLES 



the amphibia require still more than those of fish, for the sub- 

 stance of these vesicles being thicker, and more coloured in 

 man and in quadrupeds, than in the amphibia, is therefore later 

 in being dissolved in water ; and being thinnest in fish (cm), 

 it thence most readily dissolves. Those who are desirous 

 of repeating these experiments, had best begin with the blood 

 of toads and frogs, whose vesicles are large, and remain some 

 time without dissolving in the water (when that is used with 

 the above-mentioned precaution) ; by which means any one 

 accustomed to microscopical experiments may readily be satis- 

 fied of these curious circumstances. 



From the greater thickness of the vesicles in the human 

 subject, and from their being less transparent when made 

 spherical by the addition of water, and likewise from their 

 being so much smaller than those of fish or frogs, it is more 

 difficult to get a sight of the middle particle, rolling from side 

 to side in the vesicle, 1 which is become round; but with a 

 strong light, and a deep magnifier, I have distinctly seen it in 

 the human subject (civ), as well as in the frog, toad, and skate. 



Since water makes these particles round, and makes the dark 

 spot in their middle disappear, it is evident the red particles of 

 the human blood are not perforated ; but that dark spot is 

 owing to something else than a hole ; and this is likewise con- 

 firmed, by observing that although the particle does, in an ob- 

 scure glass, appear only to have a dark spot, which might be 

 supposed to have a hole, yet with a very transparent lens, and 

 a good light, after diluting the blood with serum, that middle 

 part can be distinctly seen to be only of a deeper red than the 

 rest of the vesicle, and thence appears darker. 



In these experiments, made by adding water to the blood, 

 the middle particles appear to be less easily soluble in water 

 than the flat vesicle which contains them : so that a little time 



1 These experiments were all made with daylight, in clear weather. 



(CUT.) The vesicle is certainly much more tender and evanescent 

 in fish than in birds or reptiles, as described in my paper on the blood- 

 corpuscles of British ophidian reptiles, * Proceedings of the Zoological 

 Society,' 1842, p. 108 ; but in the two last-named classes the vesicle has 

 generally appeared to me to be stronger and thicker than in mammalia. 



(civ.) See Notes xcvi and en. 



