THE GENERAL LIFE PROCESSES 327 



sugar in the seed, this sugar passes in solution to the pro- 

 toplasts that are working. Then follows the very fun- 

 damental process called assimilation. The protoplast in 

 manufacturing things is constantly transforming its own 

 substance, and therefore must constantly be renewed. 

 Therefore it receives the sugar and other foods that come 

 to it and makes protoplasm out of them. Of course this is 

 a very complicated process, and we do not know how it 

 is done. We do know, however, that it is done by a series 

 of many steps, the substances becoming more and more 

 complex, until protoplasm is reached. The ordinary food 

 substances nearest to protoplasm are the proteids, and the 

 sugars and starches (carbohydrates) must be built into 

 proteids on their way to protoplasm. Briefly stated, there- 

 fore, assimilation is the transformation of food into proto- 

 plasm, and thus the working protoplasts are perpetually 

 renewed. 



This brings us to the most important and least under- 

 stood of all the living processes. It is called respiration, 

 but the name is in such common misuse that it is more apt 

 to deceive than to explain. The protoplasm works by 

 constructing things from its own body, and in this breaking 

 up of its body to form simpler compounds oxygen takes an 

 important part, and this oxygen is taken in from the air. 

 Among the simpler compounds produced some are wastes, 

 among which the gas, carbon dioxide, which escapes into 

 the air, is most conspicuous. On account of this fact 

 respiration is often described as the taking in of oxygen 

 and the giving out of carbon dioxide, but this exchange of 

 gases is only the external indication that respiration, the 

 breaking up of protoplasm, is going on. Respiration is 

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