VITAL PROCESSES I I 



" sisters " to one another. We must bear in mind that in this 

 self-sacrificing maternity the mother is resolved into her children, 

 and her very existence is lost in their production. The above 

 phenomena, irritability, motility, digestion, nutrition, growth, 

 reproduction, are all characteristic of living beings at some 

 stage or other, though one or more may often be temporarily or 

 permanently absent ; they are therefore called " vital processes." 



If, on the other hand, we violently compress the cell, if we 

 pass a very strong electric shock through it, or a strong con- 

 tinuous current, or expose it to a temperature much above 45 C, 

 or to the action of certain chemical substances, such as strong 

 acids or alkalies, or alcohol or corrosive sublimate, we find that 

 all these vital processes are arrested once and for all ; hence- 

 forward the cell is on a par with any not-living substance. 

 Such a change is called " death," and the " capacity for death " 

 is one of the most marked characters of living beings. This 

 change is associated with changes in the mechanical and optical 

 properties of the protoplasm, which loses its viscidity and becomes 

 opaque, having undergone a process of ^-solution ; for the water 

 it contained is now held only mechanically in the interstices of 

 a network, or in cavities of a honeycomb (as we have noted 

 above, p. 5), while the solid forming the residuum has a refractive 

 index of a little over 1*6. Therefore, it only regains its full 

 transparency when the water is replaced by a liquid of high 

 refractive index, such as an essential oil or phenol. A similar 

 change may be effected by pouring white of egg into boiling 

 water or absolute alcohol, and is attended with the same optical 

 results. The study of the behaviour of coagulable colloids has 

 been recently studied by Fischer and by Hardy, and has 

 been of the utmost service in our interpretation of the 

 microscopical appearances shown in biological specimens under 

 the microscope. 1 



1 A. Bolles Lee, in his MicrotomisV s Vade Mecum, 1st ed. (1885), pointed out 

 that "Clearing reagents are liquids whose primary function is to make microscopic 

 preparations transparent by penetrating amongst the highly refractive elements of 

 which the tissues are composed, having an index of refraction not greatly inferior 

 to that of the tissues to be cleared" (p. 213). We showed later ("The State in 

 which Water exists in Live Protoplasm," in Rep. Brit. Ass. 1889, p. 645, and 

 Joum. Roy. Micr. Soc. 1890, p. 441) that since the refractivity of living proto- 

 plasm is only 1*363-1 *368, it follows that the water in the living protoplasm is in 

 a state of perfect physical combination, like the water of a solution of gum [read a 



