220 



GENERAL PHYSIOLOGY 



in the plate. A picture full of interest for every observer will then 

 be presented (Fig. 86). The much-branched network of the capil- 

 lary system is seen, and in it the blood flows with its apparently 

 yellow corpuscles so slowly that one can easily follow every indi- 

 vidual corpuscle as it winds its way in the clear plasma through 

 the fine canals and sinuosities. 



Even in the single cell such passive movements are found. 

 The fine granules that lie embedded in the protoplasm of the 

 naked cells of rhizopods show a streaming movement, especially in 

 the long, thread-like pseudopodia of marine species ; this so-called 

 granidar streaming presents a spectacle as fascinating as the 

 streaming of the blood in the capillaries, although going on much 

 more slowly. Like pedestrians in the street, or like ants, the 



granules take their self- 

 established paths, now in a 

 centrifugal, now in a cen- 

 tripetal direction, now 

 standing still, now turning 

 about, and now again pro- 

 ceeding. This granular 

 streaming does not come 

 about by the active pro- 

 gressive movement of the 

 granules themselves ; but 

 by their being passively 

 dragged along by the liquid 

 protoplasmic ground -sub- 

 stance in which they lie 

 embedded, and which has 

 constantly an active flowing 

 motion. 



Another interesting form 

 of passive movements that occur in the living cell is the so-called 

 Brownian molecular movement. There lives in fresh water a small, 

 unicellular, green alga, Closterium, of a delicate crescent-shape 

 (Fig. 87, /). In its protoplasm at each end of its body is a vacuole 

 of liquid, in which as a rule lie fine granules which show Brownian 

 motion By strong magnification it may be seen that the granules 

 are continually dancing about each other with a delicate trembling 

 motion, but without moving to any considerable distances. The 

 dancing continues tirelessly and unceasingly. Here the object in 

 which this peculiar motion is seen is living. More frequently, how- 

 ever, it can be observed in dead cells, and it has long been known 

 in the so-called salivary corpuscles in the saliva, which are dead 

 leucocytes (white blood-corpuscles). These leucocytes are swollen 

 into a spherical form by the absorption of water, and possess a 

 nucleus surrounded by granular protoplasm (Fig. 87, II\ 



■Pia. 



-Capillary circulation in the web of the frog's 

 foot. (Alter Ranke.) 



