178 LIFE AND DEATH. 



which are being constantly studied by the chemist. 

 They also are to be found in great variety. It has 

 been difficult to separate them one from the other, to 

 characterize them rigorously, or, in other words, to 

 classify them. However, it has been done now, and 

 we distinguish three classes which are differentiated 

 at once from the physiological and from the chemical 

 points of view. The first comprises the complete or 

 typical albuminoids. They are the proteids or micleo- 

 albiiminoids. They are to be found in the most active 

 and most living parts of the protoplasm, and therefore 

 in the spongioplasm of the cell and around the 

 nucleus. The second group is formed of albumins 

 and globulins, compounds already simpler, fragments 

 derived from the destruction of the preceding, into 

 which they enter as constituent elements. In the 

 isolated state they do not belong to the really living 

 protoplasm; they exist in the cellular juice, in the 

 interstitial and circulating liquids in the blood and in 

 the lymph. The third category comprises real but 

 incomplete albuminoids. They are to be found in 

 the portions of the economy which have a specialized 

 or attenuated life, and are destined to serve as a 

 support to the more active elements — i.e., they con- 

 tribute to the building up of the bony, cartilaginous, 

 conjunctive, elastic tissues. They are called albii- 

 moids. It is naturally the first group, that of the 

 proteids — i.e., of the complete and characteristic com- 

 pounds of the living substance — upon which the 

 attention of the physiologists must be fixed. It is 

 only quite recently that the clear definition of these 

 substances has been given, and proteid compounds 

 detected in the confused mass. 



The Nucleo-proteids. — This progress in the char- 



