70 DIFFUSION OF SUBSTANCES INTO LIVING CELLS 



Conversely, in a given time, the greater the con- 

 centration of the substance diffusing, the more of that 

 substance will pass into the cell, as was shown in the 

 first law. We have now considered two factors, there- 

 fore, viz. that diffusion is equal to the concentration of 

 the substance and the time, or thus: 



diff = S+T 



The next factor to be considered is heat. In vivo, 

 of course, variations of temperature are not very great, 

 but with in-vitro experimentation the temperature must 

 be carefully considered, for we may keep the slide with 

 its jelly-film with which we are working at a variety of 

 temperatures, ranging from that of the room in which 

 one works to that of the blood. Heat increases the 

 diffusion of substances into cells in a marked degree, 

 and this increase is also in arithmetical proportion. 

 Each degree of temperature means a definite increase in 

 the diffusion, and therefore the diffusion can be regu- 

 lated to a nicety by keeping the slide on which the cells 

 are resting at a definite temperature. Of course if 

 extremes of heat are used death will occur; but within 

 reasonable limits, which are compatible with life, one 

 can employ heat to great advantage in these experi- 

 ments. H eat therefore must be coupled with concentra- 

 tion and time as a factor which increases diffusion; and 

 our equation now stands thus: 



diff = S + T + H 



There is one other factor which increases the diffusion 

 of substances into cells more than any of the three other 



