58 HISTOLOGY OF NUTRIENT /-7J77)S. 



The amoeboid movements of these leucocytes may be seen 

 in human blood by using a warm stage at nearly the normal 

 heat. The blood of a frog, or other cold-blooded animal, 

 needs no warm stage. The movements of leucocytes show 

 varying degrees of vitality. Some are active, others sluggish, 

 and some inert or moribund. Some contain fat molecules 

 similar to the pus cells in inflammation, and main* dormant 

 cells may be quickened by gentle stimulation. 



Leucocytes absorb a great variety of things, as milk, oil, 

 carmine, aniline blue, etc. Kven red corpuscles may be swal- 

 lowed by them, and they have been seen to devour one an- 

 other. Some bacteriologists regard them as destroyers of 

 microbes in the blood, under the term "phagocytes," and con- 

 sider them to promote immunity from many diseases. Their 

 migration through the walls of blood vessels, and their part 

 in the building of tissues, forms an important factor in pathology 

 as well as physiology. 



IV. RED BLOOD CORPUSCLES. 



First seen by Swammerdam, in 1658, and in human blood 

 by Lewenhceck, in 1673. More observed than any other 

 structure, yet only partially known, since their formation re- 

 quires perfect objectives and unusual skill. Most of the mis- 

 takes made in histology arise from the employment of too low 

 powers. Thus the red blood corpuscles have been variously 

 described as rings and as simple homogeneous flat discs. 

 Better microscopes and greater care teach us more. 



I. Form and color. Under moderate powers the red cor- 

 puscles of human blood appear usually as flattened discs, with 

 rounded edges and depressed centers. Fig. 3, PI. 3. They 

 are generally circular in mammals, except the camel and llama, 

 which have elliptical discs. They are also elliptical in birds, 

 amphibia, and fish, except a few fishes of the order cyclostoma, 

 which have circular discs. With higher powers both the cir- 

 cular and elliptical discs are seen to be quite irregular, and 

 even polyhedral in outline. The color of the red corpuscles is 

 due to hemoglobin, which is infiltrated in the filmy framework, 

 or stroma, and forms more than 90 per cent of their organic 



