THE BLOOD 183 



3. As moving cells they wander about from the lymph to 

 the blood, or vice versa, and even into the intestines, carrying 

 with them dead matter to be eliminated, or crowding in large 

 numbers and producing some special substances that counteract 

 a local chemical disturbance. 



Because of this peculiar behavior we have come to think 

 of these corpuscles as perhaps the most important agents in 

 keeping the body in health, at least in relation to certain 

 special diseases. 



White corpuscles probably originate by the division of ameboid 

 cells in the bone-marrow and in particular portions of the lymphatic 

 system, enlarged lymph spaces containing crowds of the white 

 corpuscles. 



214. The red corpuscles. The blood of vertebrate animals 

 contains red corpuscles in addition to the white ones. In all 

 except the mammals the red corpuscle has a nucleus in the 

 center, which makes the disc somewhat thicker in the middle, 

 and its shape is elliptical rather than circular.^ The largest 

 red corpuscles are found in the amphibia ; and even with the 

 lower power of the microscope we may easily see the elliptical 

 discs in the flowing blood of a frog's web or a tadpole's tail. 



The distinctive thing about the red corpuscle is the fact that 

 it contains a substance known as hemoglobm, which readily 

 combines with oxygen or with carbon dioxid, according to the 

 chemical conditions to which it is exposed. The red corpuscle 

 thus acts as a gas-carrier in the blood. 



Recent experiments made in this country show that there is a 

 special ferment in back-boned animals which causes the hemoglobin 

 to combine with oxygen in the lungs (or gills), and that there is 

 another ferment which causes the oxygen-hemoglobin combination to 

 break up in all parts of the body. 



^ Among the mammals, the camel is exceptional in having elliptical blood 

 corpuscles. Among the fishes, the perch and a few others have circular 

 corpuscles. 



