Chap. III.] THE PROCESS OP AGGREGATION. 53 



cut off close beneath the glands, by the glands absorbing 

 various fluids or matter dissolved out of certain bodies, by 

 exosmose, and by a certain degree of heat. On the other 

 hand a temperature of about 150 Fahr. (65.5 Cent.) does 

 not excite aggregation; nor does the sudden crushing of a 

 gland. If a cell is ruptured, neither the exuded matter nor 

 that which still remains within the cell undergoes aggrega- 

 tion when carbonate of anunonia is added. A very strong 

 solution of this salt and rather large bits of raw meat pre- 

 vent the aggregated masses being well developed. From 

 these facts we may conclude that the protoplasmic fluid with- 

 in a cell does not become aggregated unless it be in a living 

 state, and only imperfectly if the cell has been injured. We 

 have also seen that the fluid must be in an oxygenated state, 

 in order that the process of aggregation should travel from 

 cell to cell at the proper rate. 



Various nitrogenous organic fluids and salts of ammonia 

 induce aggregation, but in different degrees and at very 

 different rates. Carbonate of ammonia is the most power- 

 ful of all known substances; the absorption of it^^i^^ of a 

 grain (.000482 mg.) by a gland suflSces to cause all the cells 

 of the same tentacle to become aggregated. The first effect 

 of the carbonate and of certain other salts of ammonia, as 

 well as of some other fluids, is the darkening or blackening 

 of the glands. This follows even from Ibng immersion in 

 cold distilled water. It apparently depends in chief part on 

 the strong aggregation of their cell-contents, which thus 

 become opaque and, do not reflect light.* Some other fluids 

 render the glands of a brighter red; whilst certain acids, 

 though much diluted, the poison of the cobra-snake, fec., 

 make the glands perfectly white and opaque; and this seems 

 to depend on the coagulation of their contents without any 

 aggr^ation. Nevertheless, before being thus affected, they 

 are able, at least in some cases, to excite aggregation in 

 their own tentacles. 



ments of the protoplnsm, nnd wnlls; thon^^h no doiiht th> ef- 

 pven dPtermlnes Its soparntlon fects of pressure or of a touch 

 from the wnlls. But the process on the outside must be trans- 

 of aKf^reg^tlon Is a different phe- mitted through this Inyer. 

 nomenon. ns It relates to the [The words " which .... 

 contents of the cells, and only light " would probably have been 

 secondarily to the Inyer of proto- omitted bv the author In a sec- 

 plasm which flows along the ond edition. F. D.] 



