140 VIEWS OF THE MICROSCOPIC WORLD. 



magnitude of the globule. In figure 239, the red disks of the human blood are 

 F . delineated as they are revealed when subjected to a hi^h 



r ig. xjy. , ,, . * _,, > o 



magnifying power. I hey are here seen promiscuously scat- 



tereC * OVer ^ ie sur ^ ace ' though tne 7 ai *e often beheld united 

 together l.y their flat surfaces, and forming little bead-like 

 rows of crimson atoms. The central depression is distinctly 

 visible in the several atoms. The size of the red globules 

 ^ s sll bject to much. variation, even in the same animal. In 

 human blood it ranges, according to the best authorities, from 

 one- thirty -jive hundredth part of an inch to one-forty-jive 

 hundredth, though an eminent observer has found their 

 average diameter to be as great as one-twenty eight hundredth of an inch. 

 Their size in the elephant is about one-twenty-seven hundredth of an inch, and 

 in the napu-musk deer only one-twelve thousandth. 



The blood-disks in birds, reptiles, and fishes, differ from those of Mammalia, in 

 being larger, and their shape is also oval instead of round; moreover, in place of 

 being depressed at the middle, they swell out on either side, owing to the fact 

 that the centre of the atom is composed of matter more solid than the other 

 portions. In birds, the length of the oval disk varies from one-seventeen hun- 

 dredth of an inch to one-twenty-four hundredth, and the breadth from one-three 

 thousandth of an inch to one-forty-eight thousandth. In the case of frogs, the 

 longer diameter is about one-thousandth of an inch in extent, while in fishes 

 these globules are for the most part larger than those of the frog. The white 

 globules in man and the Mammalia, are usually larger than the red, but like the 

 latter, they differ in magnitude. Their average size, when examined in the blood, 

 is estimated at about one-twenty-six hundredth part of an inch. In the blood of 

 reptiles, and in that of the frog in particular, the relation that exists as to size be- 

 tween the red and white globules, is reversed ; the latter being in these cases 

 two or three times smaller than the former. These two classes of atoms differ 

 also in respect to form, since the white blood particle is always globular through- 

 out the whole animal kingdom : a nucleus, consisting of matter more solid than 

 the rest, is also found in the white globule, instead of a central depression as 

 detected in the red. 



The third class of atoms, termed molecules, have been regarded as the ele- 

 ments out of which the other two kinds are formed. They are found in great 

 quantities amid the blood, existing singly, and also in small masses of an irregular 

 form. Their minuteness far surpasses that of the other atoms, since they scarcely 

 ever exceed in diameter one-thirty thousandth part of an inch. 



THE WEB OF THE FROG'S FOOT. When the web of a frog's foot is examined 

 with a high magnifying power, it exhibits a beautifully tesselated ground, inter- 

 sected by blood-vessels and minute capillaries, that wander over its surface. In 

 these the circulation of the blood is distinctly seen, the fluid coursing swiftly 

 through the arteries, but moving with less velocity through the veins. The red 



