THE BLOOD. 



35 



If the web of a frog's foot is spread out and examined under the microscope, 

 the blood is seen to flow in a continuous stream through the vessels, and the 

 corpuscles show no tendency to adhere to each other or to the wall of the vessel. 

 Doubtless the same is the case in the human body ; but when drawn and examined 

 on a slide without reagents, the blood-globules often collect into heaps like 

 rouleaux of coins (Fig. 1, c). 



During life the red corpuscles may be seen to change their shape under pres- 

 sure - adapt themselves to some extent to the size of the vessel. They are 

 also highly elastic, for they speedily recover their shape when the pressure is 

 removed. They are soon influenced by the medium in which they are placed, 

 and by the specific gravity of the medmm. In water they swell up, lose their 

 shape, and become globular ; subsequently the haemoglobin becomes dissolved out. 

 and the envelope can be barely distinguished as a faint, circular outline. Solu- 

 tions of salt or sugar, denser than the serum, give them a stellate or crenated 

 appearance : and the usual shape may be restored by diluting the solution to the 

 proper point. The same crenated outline may be produced as the first effect of 

 the passage of an electric shock ; subsequently, if sufficiently strong, the shock 

 ruptures the envelope. A solution of salt or sugar of the same specific gravity as 

 serum merely separates the blood-globules mechanically without changing their 

 shape. 



The white corpuscles (Fig. 2) are rather larger than the red in human blood, 

 measuring from about 2innr to a ^ 0o of an inch in diameter. They consist of a 

 transparent granular-looking protoplasm containing one, two, or more nuclei, and 

 presenting bright granules, which vary in different corpuscles both in quantity 

 and in their behavior to micro-chemical reagents. When absolutely at rest they 

 are rounded or spheroidal, but under 



ordinary circumstances their form is 

 very various, and they have the re- 

 markable property of undergoing 

 amoeboid " changes (Fig. 3). That 

 is to say. they have the power of send- 

 ing out finger-shaped or filamentous 

 processes of their own substance, by 

 which they move and take up gran- 

 ules from the surrounding substance. 

 In locomotion the corpuscle pushes out a process of its substance a pseudopodium, 

 as it is called and then shifts the rest of the body into it. In the same way, 

 when any granule or particle comes in its way it wraps a pseudopodium round it, 



FIG. 2. a. White corpuscles of human blood, 

 corpuscles. High power. 



d. Red 



FIG. 3. Human colorless blood-corpuscle, showing its successive changes of outline within ten 

 minutes when kept moist on a warm stage. (Schofield.) 



and then, withdrawing it. lodges the particle in its own substance. By means of 

 these amoeboid properties they have the power of wandering or emigrating from 

 the blood-vessels by penetrating their coats, and thus finding their way into the 

 perivascular spaces. 



The white corpuscle may be taken as the type of a true animal cell. It has 

 no limiting membrane, but consists of a mass of transparent albuminous substance, 

 called protoplasm, containing one or more nuclei. These nuclei may assume 

 varvinc: shapes, being sometimes spherical, sometimes horseshoe-shaped, some- 

 times moniliform. these various shapes being transition stages between the mono- 

 nuclear and polynuclear corpuscles. 



The white corpuscles are very similar to, if not identical with, the corpuscles 

 of lymph and chyle, and they also bear a strong resemblance to the cells found 



