142 BIOLOGY. [BOOK IT. 



question it is very easy to show : verily the chlorophyllian cell 

 makes starch, and probably protei'c substances, by combining the 

 elements of the atmosphere and those of the ascending sap. 

 Verily, also, there are in animal organisms cells which fabricate 

 an amyloidal substance, either by isomeria or by synthesis. All 

 the rest is in a state of hypothesis. 



A very certain fact is, that animals cannot aliment themselves 

 without substances already elaborated either by plants or by 

 other animals, and that it will be the same with man, as long as 

 chemistry cannot fabricate completely, synthetically, the im- 

 mediate organic and complex principles of which he stands 

 in need. 



The synthesis of albuminoidal substances seems as if it would 

 baffle the science of the chemist for some time longer. Never- 

 theless, these substances are supremely the materials of life ; 

 but their mobility, their instability, that is to say the very 

 qualities which render them suitable to form living anatomical 

 elements, are serious obstacles not only to their artificial fibrica- 

 tion, but even to the determination of their formula, and, up to 

 the present time, chemistry has only succeeded in synthetizing 

 hydrocarburates, or regressive azotized bodies, of which urea is 

 the type. 



A very important property of the coagulable albuminoidal 

 substances proceeds from their very mobility ; it is the faculty 

 M-hich they have of transmitting to each other in living organisms 

 and by simple contact their molecular conditions. These are only 

 simple isomeric changes, and it is by this process that each 

 anatomical element, whatever may be its composition, fabricates, 

 at the expense of the plasmas, of the common nutritive juices, 

 the special compounds which it must assimilate. 1 



After the same manner also we may explain the action of the 

 different kinds of virus, as well as hereditary transmission and 

 morbid contagion. 



We may observe analogous phenomena in protei'c substances 

 1 Ch. Robin, loc. tit., Introduction, p. xiii, 



