IX. METABOLISM 295 



particle cannot incorporate amino acid, but that it can only be achiev- 

 ed in the presence of complete energy supplying systems. 



Since each type of protein molecules may be able to act as each 

 type of enzyme systems as already suggested, such cooperation of a 

 variety of particles for a common purpose may mean the establishment 

 of an enzyme system for the protein synthesis. Rickettsiae are com- 

 posed of a number of virus-like particles or elementary bodies, which 

 may be different from each other in their physical and chemical pro- 

 perties, and hence the enzyme system may start to function and thus 

 a certain type of Rickettsiae can proliferate outside the host. 



The fact that some bacteria can recover their complete form 

 after being decomposed into virus-like particles, may appear to show 

 that each particle shares the faculty of synthesizing proteins. Yet, 

 this seems not to be the case. Separated single particle cannot grow 

 as above considered. In order to multiply, decomposed particles 

 having various properties may have to unite with one another into 

 larger masses ; only in this way they may be able to accomplish the 

 synthesis. 



It has already been stated that virus-like protoplasm particles 

 can be fused in vitro into cell-like masses. This may be looked upon 

 as a restitution of the original cell mass. A remarkable example of the 

 restitution of body form and function has been found with sponges 

 and hydroids (66). These organisms were cut into small fragments 

 and then pressed through the meshes of fine bolting cloth. In this 

 way the flesh was broken up into very small fragments. Shortly 

 after the operation many of the isolated elements were observed to 

 have fused together into lumps or sheets of tissue. Soon larval stages 

 arose very similar to the typical normal larva. Ultimately new com- 

 plete adults developed. 



Such a reversible decomposition of cells or organisms is probably 

 based upon the general reversibility of protein structure. As repeated- 

 ly emphasized, the reversibility involved in the nature of protein is 

 of the utmost importance in developing the various reversible charac- 

 ters in living substances. This reversible decomposition may be only 

 one of these examples. It was found that haemocyanin, the copper- 

 containing respiratory chromoprotein of invertebrates, is split into 

 subunits of one half or one eighth of the original molecular weight 

 by exposure of the protein solution to pH 8.5, and that reassociation 

 by exposure of the protein solution to pH 8.5, and that reassociation 

 at pH 6.85 to form the original units occurs quite specifically. Frag- 

 ments of haemocyanin from Helix pomatia recombine with fragments 

 of the same haemocyanin, but not with fragments derived from the 

 haemocyanin of Littorina littorea (128). Various evidences of such 



