498 PROTOPLASM 



forms of coagulation that we have so far considered. When 

 bacteria agglutinate, they play no active part as living particles ; 

 the mechanism involved is identical with that which brings 

 about the aggregation of nonliving particles. The agglutma- 

 tion or assembling of certain cells, however, rests, at least in 

 part, upon their own vital activities. This is the case of the 

 extraordinary " heteroagglutination " of dissociated sponge cells 

 described by Galtsoff . If cells of the sponge Microciona prolifera 

 are artificially separated, they reunite by amoeboid movement. 

 This is not in itself extraordinary, as cells aggregate to form 

 colonies or unite to form tissues; but among the individual 

 cells of the seven kinds that make up a sponge, each joins 

 its own kind. Chemical distinctions in the cells are possibly 

 responsible for this each-unto-his-own reunion. When the cells 

 of two different species are mixed, there is no mingling of the 

 two in the reorganization process. Such an agglutination or 

 assembling of cells may have certain physical and chemical 

 properties in common with ordinary coagulation processes, for 

 in the latter, while there is no superficial evidence of selective 

 arrangement, as in the case of the cells of a sponge, there is evi- 

 dence that the action of protein (blood) coagulants — in particu- 

 lar, the specificity of antigens and antibodies — is due to a definite 

 arrangement within the molecules analogous to that of the 

 lattice structure of crystals. This structural orientation may be 

 responsible for the combination of a certain antigen with a 

 certain antibody, as will be seen in a moment; it may also be 

 responsible for each cell of a disorganized sponge reuniting only 

 with a cell of its own kind. 



Protein Individuality and Specificity. — Emphasis on the pro- 

 teins as representing the most significant of the constituents of 

 protoplasm, in that they among all classes of compounds display 

 a greater number of the specific properties of life, suggests that 

 organisms are what they are because of the proteins that they 

 contain. This may, in a broad sense, be true, and it seems 

 probable, in the light of Abderhalden's and of Leathes's esti- 

 mates of the almost inconceivably great number of permutations 

 (amino-acid orientations) in proteins, that every species, if not 

 every individual, has its own specific protein or protein group. 

 It has already been suggested that important as the proteins 

 are, they may serve primarily as carriers of other even more 



