680 THE MICROSCOPE. 



and animals below them, there are nuclei ; but the cells, 

 instead of being circular, as in the human subject, are 

 elliptical, and larger. The corpuscles in Mammalia in 

 general are like those of man in form and size, being a 

 little larger or smaller. The most marked exception is iu 

 the blood of the Musk-deer, in which the corpuscles are 

 of extreme smallness, about the 1-1 2,000th of an inch in 

 diameter. The Elephant has the largest, which are about 

 1- 2,000th of an inch in diameter. The Goat, of all common 

 animals, has very small corpuscles ; but they are, withal, 

 twice as large as those of the Musk-deer. Another excep- 

 tion in regard to form is in the Camel tribe, where they 

 are oval, and resemble those of the oviparous Vertebrata, 

 as the Frog, shown in fig. 314, No. 2. In the Meno- 

 branchus lateralis, they are of a much larger size than in 

 any animal, being the 1 -350th of an inch ; in the Proteus, 

 the l-400th of an inch in the longest diameter ; in the 

 Salamander, or Water-newt, l-600th; in the Frog, l-900th; 

 Lizards, l-l,400th ; in Birds, l-l,700th ; and in Man, the 

 1-3, 200th of an inch. Of Fishes, the cartilaginous have 

 the largest corpuscles ; in the Gold-fish, they are about the 

 1-1, 700th of an inch in their longest diameter. 



The large size of the blood-discs in reptiles, especially in 

 the JBatrachia, has been of great service to the physiologist, 

 by enabling him to ascertain many particulars regarding 

 their structure which could not have been otherwise deter- 

 mined with certainty. The value of the spectroscope in 

 the chemical examination of the blood has been already 

 pointed out in our remarks on the application of this 

 instrument to the microscope. See page 119. 



An interesting subject to Physiologists has been noticed 

 the production from the blood, under certain conditions, 

 of red albuminous crystals, which, although formed from 

 animal matter, and sometimes, in all probability, during 

 life, have the same regular forms as inorganic crystals. 

 Virchow was the first who paid particular attention to 

 their actual nature, and proved them to differ from saline 

 or earthy crystals. If we add water to a drop of blood 

 spread out under the object-glass of the microscope, as the 

 drop is beginning to dry up, the edges of the heaps of blood- 

 corpuscles are seen to undergo a sudden change : a few 



