BUILDING OF LIVING MATTER 121 



a similar part with the acid part of a fourth 

 molecule. Now there are four molecules, 

 and still there are free attachments for 

 more, for each of the new molecules has a 

 free active portion. If a certain percentage 

 of the molecules so aggregating are either 

 di-basic acids, or have two amino positions to 

 act as a double base, this system can branch 

 in all directions in space. 



Accordingly, without true atomic union 

 between them, there may be ten, twenty, 

 thirty, sixty molecules forming a great 

 aggregate molecule. This is the form in 

 which proteins occur in living cells, and is 

 an example of an organic colloid. 



A most important point to note here is 

 what the chemist calls the " lability " or 

 " mobility " of such a colloid. Its strength 

 for the purposes of the vital phenomena 

 lies in its very weakness as a chemical body. 

 It exists in a state of the most delicate 

 balance, ready to play in and out, and vibrate 

 like a piece of mechanism, only far more 

 delicately, responding to every change in its 

 environment. Its dimensions as an aggregate, 

 and the constitution of its parts depend on its 

 environment, and especially upon its nutrition. 

 It must, once it has been constructed, be 

 fed with the proper pabulum, nothing must 



