OF THE BLOOD. 233 



same animal, some being a little larger than others, and some 

 dissolve in water more readily than others (cxv) . 



In the same species of animals, they even differ in size in 

 the different periods of life. In a chicken, on the sixth day 

 of incubation, I found them larger than in a full-grown hen, as 

 it is represented in Plate V, fig. 4, and I have found them larger 

 in the blood of a very young viper than in that of its mother, 

 out of whose belly it was taken (cxvi) . I have not, however, 

 been convinced from experiments that there is any difference 

 in size between those of a child at its birth and those of an 

 adult person. 



In the blood of some insects the vesicles are not red, but 

 white, as may easily be observed in a lobster (which Linnseus 

 calls an insect), one of whose legs being cut off, a quantity of 

 a clear sanies flows from it ; this after being some time exposed 

 to the air jellies, but less firmly than the blood of more perfect 

 animals. .When it is jellied it is found to have several white 

 filaments ; these are principally the vesicles concreted, as I 

 am persuaded from the following experiment. 



EXPERIMENT IV. 



If one of the legs of a lobster be cut off, and a little of the 

 blood be catched upon a flat glass, and instantly applied to 

 the microscope, it is seen to contain flat vesicles, that are cir- 



(cxv.) Hewson here justly notices the difference in corpuscles of the 

 same blood. They are not all affected in the same manner by acetic 

 acid ; neither are they all exactly alike in form ; nor as to the presence 

 or absence of the nucleus. If considered as floating glandular cells, 3 

 they must be constantly changing from the time when they are first 

 formed to that when they finally melt in the plasma. 



(cxvi.) Hewson has also correctly depicted the round form of the 

 corpuscles of the embryo of oviparous vertebrata, Plate V, figs. 4 and 7. 

 In the very young embryo of mammals, the corpuscles are much larger 

 than in the adult. At a later period, when the nucleus b has generally 

 disappeared, the corpuscles of the fcetus are still larger and more un- 

 equal in size than those of the mother ; and from the last fact it is 

 difficult to ascertain, at a yet later term of mtra-uterine life, whether 

 they he larger or smaller in the fcetus than in the adult. In a kid, 

 twelve days old, bred between an ibex and a goat, I found the corpuscles 

 larger and more variously sized than those of either of its parents. See 

 the Tables of Measurements at the end of this chapter, Note cxvin*. 



a See Note cxvin, p. 235. b See Notes en and cxxxvu. 



