36 DURATION OF THE SEVERAL MITOTIC STAGES 



chemical reactions with the phenomena of growth. It does not, how- 

 ever, take into consideration the differential effect of heat at different 

 temperatures, nor the possibility of physical shock in raising and lower- 

 ing the temperature, nor the possible wastage and excretion of products 

 before the measured stage is reached. 



Ward^ calls attention to a fact of interest to those who seek to estab- 

 Ush physiological constants, namely: 



"That the variation in rate of growth which has been going on at an hith- 

 erto constant temperature is more pronounced when the rise or fall is 2° C. than 

 when it is only 1° C. will be obvious, and similarly for any other range; but, 

 again, it must be noted that the amount of deflection of the curve for any 

 range of variation depends on the amount of temperature, or the hitherto con- 

 stant temperature at which the growth has been going on The external 



factors are : (1) Temperature. Variations in the curve are produced by sudden 

 variations in the temperature, and apparently the variations are the more 

 pronounced the quicker the temperature changes and the more extensive their 

 range; but the amount of variation in the curve due to any given rise or fall of 

 temperature in constant time appears to depend on the distance of the tem- 

 perature (from which the variations is reckoned) from the optimum. In other 

 words, the sensitiveness of the organism to a rise or fall of a degree centigrade 

 varies according to the temperature from which the rise or fall occurs; for if it 

 has been growing at 30° C. constant temperature, for an hour, it shows a more 

 marked deflection in the curve for a sudden rise or fall of 1° C. than for the 

 same sudden rise or fall from 25° C." 



He then discusses other factors wdth which we are here not so con- 

 cerned. 



C. NATURE OF THE COMPLEX IN GROWTH AND MITOSIS. 



Physiologists often have attempted to treat the complex of bulk 

 increase and mitotic activity as a unit, fitting in its end-product the 

 simple formula followed by reactions in homogeneous chemical systems. 

 If, by any chance, in a special case, growth (impljdng an alternation in 

 (a) the absorption of food materials, cell turgor, and (6) mitotic poten- 

 tial and its consequent mitosis) should be found to follow the same rule 

 in response to one or more external agents as is obeyed by the simpler 

 organic reactions, it would indeed be a matter of chance and not an 

 homologous response due to types of chemical activity being parallel 

 throughout. The one is a relatively simple and direct reaction, and the 

 other a vast complex of inhibitions and activations, with their interplay, 

 giving finally a single measurable resultant of forces. In mitosis we 

 see different structures and can trace their dissolution and reorganiza- 

 tion; this shows clearly that mitosis is not a homogeneous chemical 

 reaction. There are many different substances distributed throughout 

 the cell, but their distribution is not so homogeneous as not to require 

 the consideration of the diffusion factor before completing their chem- 

 ical reactions incident to mitosis. The fact that different structures and 

 substances in the cells, both Uving and dead, take different stains proves 



1 See ref. No. 1, p. 13. 



