218 HISTORY OF BOTANY 



solved we must despair of acquiring any real conception 

 of what protoplasm itself is, and any clear idea of what 

 is meant by the term " life/' 



Not a few biologists have indulged in speculations 

 on the subject, such as the human physiologist Pfiiiger 

 in 1875, Loew and Bokorny in 1892, and Verworn two 

 years later, but as these speculations would be meaning- 

 less to you at the present stage in your studies, I do 

 not think there is anything to be gained by recount- 

 ing them. Emil Fischer's work on the constitution 

 of proteins belongs to a somewhat later period, but 

 perhaps I may make a very brief reference to it here. 

 Fischer showed that proteins, animal as well as vegetable, 

 may be split into amino-acids, after the elimination 

 of water. An amino-acid in turn is composed of a 

 grouping of nitrogen and hydrogen atoms NH 2 - 

 with a grouping of carbon, oxygen, and hydrogen atoms 

 COOH known as carboxyl. If water (H 2 O) be elimin- 

 ated there is left CO NH, which chemists call a " pep tide 

 linkage." The various amino-acids are composed of one 

 or more NH 2 groups united with one or more COOH 

 groups, and Fischer was able, after elimination of the 

 water molecules, to form artificially a large number 

 of peptides containing two or more amino-acids, and 

 the suggestion is that these bodies are stages in the 

 construction of the complex we call protoplasm. 



KATABOLISM 



In the animal world the intaking of oxygen and the 

 exhalation of carbon dioxide, commonly known as 

 " respiration," had, from a very early date, been recog- 

 nised as associated with the exhibition of vital phenomena 

 and the expenditure of energy, but it was not until the 

 earlier years of the nineteenth century that physiologists 

 distinguished between the obvious external gaseous 

 interchange and the actual chemical processes taking 



