PROCESSES OF LIFE REVEALED BY THE MICROSCOPE. 393 



is manifested by the little cilia. These sweep with almost incredible 

 rapidity in one direction and more slowly on their return, thus produc- 

 ing a current in the direction of most rapid motion. This motion with 

 the resulting current ceases only with life. Each individual cilium is 

 weakness itself, but with their combined action the untold millions 

 covering the cells, in the air passages for example, make a strong cur- 

 rent in the liquid covering them. This current is from the interior of 

 the lungs toward the throat and carries along with it particles of dust 

 inhaled into the lungs. In this way the delicate breathing organs are 

 swept clean and left unincumbered for their work of receiving oxygen 

 and getting rid of carbon dioxide. 



If now one puts under the microscope some cells from the small 

 intestine of almost any animal from the lamprey eel to man, the cells 

 appear almost identical with those just described. The end projecting 

 to the free surface of the intestine seems to have a similar brush of 

 fine hairs, with a clear line along their base. If a striated and a dead 

 ciliated cell are under the same microscope side by side, it is almost 

 impossible to distinguish them. Indeed so difficult is it that those from 

 the intestine have been described as ciliated more than once. If both 

 cells are living, no one could confuse them. The striated end of one is 

 motionless, the lines or cilia of the other are in constant motion. One 

 serves for producing currents, always in the same direction, the other 

 is for the purpose of absorbing and passing into the tissues the products 

 of digestion. One is a moving the other an absorbing cell. (See Plate 

 XVI.) 



Most of the tissue elements of the higher forms can not be thus 

 studied alive, however, and the best that can be done is to fix the dif- 

 ferent phases of action, as by a series of instantaneous photographs, 

 then with a kind of mental kinetoscope put these together and try to 

 comprehend the whole cycle. 



Fortunately for the histologist the incessant experbnentation of the 

 last twenty-five years has brought to knowledge chemical substances 

 which do for the tissues the wonder that was ascribed to the mythical 

 Gorgon's head — to kill instantly and to harden into changeless perma- 

 nence all that gazed upon it. So the tissues may be fixed in any phase 

 and then studied at length. If then the investigator observes and 

 keeps record of every point that may have an influence on the struc- 

 tural appearances, whether shown by experience or suggested by 

 insight, and this record always accompanies the specimen, thus and 

 thus only, it seems to me, can he feel confident that he is liable to gain 

 real knowledge from the study, knowledge that represents actuality, 

 and which will serve as the basis for a newer and more complete unrav- 

 eling of the intricacies of structure, an approximate insight into the 

 mechanism through which the life energy manifests itself. 



And so, with all the life that physics and chemistry can give, com- 

 mencing with the simplest problems and being careful that every factor 



