MAXUAL OF HISTOLOGY. 



disk-like form and assume a spheroidal, perhaps spherical con- 

 tour. The coloring matter then escapes, in most instances, and 

 they become quite transparent (see Fig. 17). Such corpuscles are 

 often seen in human urine where they appear as colorless rings. 

 In frog's or newt's blood the body of the disk first imbibes the 



Fro. 17. Human red blood-globules: 

 a, with haemoglobin ; 6, without it (Rol- 



l3tt.) 



FIG. 18. Red corpuscles of the frog 

 that have imbibed water. (Rollett.) 



water ; later, the nucleus, which then has a sharply defined 

 outline. Sometimes the material of which the body is largely 

 composed (haemoglobin) is gathered about the nucleus, sending 

 off radiating prolongations to the periphery, while the imbibed 

 fluid is stored in the intervening spaces (see Fig. 18). 



Action of carbonic acid gas. This experiment requires a 

 special apparatus. First of all it is essential to have a moist 

 chamber (Fig. 19). 



Take a small, flat bit of wood about 1| inch wide, 3 inches 

 long, and f inch thick ; make a square opening in the centre, 

 sufficiently large to admit an ordinary inch cover-glass ; this 

 is to be pressed to the bottom and firmly fixed, thus making a 



shallow well with a glass 

 bottom. Into this cham- 

 ber are admitted, through 

 side holes, glass tubes (one 

 on each side), so that air 

 or gases can be carried into the chamber. When in use, the 

 chamber is kept moist by a drop of water, which is put in 

 one corner of the well, while the specimen of blood to be ex- 

 amined is dropped upon a large glass cover, and the latter in- 

 verted over the mouth of the well. In determining the effect 

 of carbonic acid gas upon animal life, we have merely to con- 

 nect the gas-chamber just described with a jar in which carbonic 



Fio. 19. Moist chamber. 



