172 



SCIENCE 



[N. S. Vol. XXXIII. No. 840 



the same time these products are fre- 

 quently very nutritious for cells of a differ- 

 ent sort and alcohol furnishes a most suit- 

 able pabulum for the organisms which 

 produce vinegar. Vinegar in its turn is 

 toxic to the microbe which produces it, but 

 serves again as a soil for another which 

 gives rise to a viscous fermentation. By 

 the successive action of these ferments a 

 solution of sugar may produce, first, al- 

 cohol, secondly, vinegar, and thirdly, ropy 

 mucus. In this particular series each 

 microbe produces a substance injurious 

 to itself but useful to its successor. This 

 is, however, not always the case be- 

 cause a cell may produce a substance 

 not only injurious to itself but injurious 

 to other cells, and alcohol in large quantity 

 not only kills the cells of yeasts, but other 

 cells as well. Similar conditions occur 

 within living organisms where the cells 

 composing the different parts are con- 

 nected together and pass on the products 

 of their life from one cell to another by 

 means of the circulation of the blood and 

 tissue juices. The secretions of one part 

 may be, and indeed generally are, useful 

 to other parts of the organism and so long 

 as no part sins, either by deficiency or ex- 

 cessive action, the whole organism main- 

 tains a condition of health. But this is not 

 always the case and health may be de- 

 stroyed by (a) excessive, (&) defective or 

 (c) prevented action of one or more of the 

 parts composing the body." 



Vernon^^ has tested the influence of the 

 excreta of adult eehinoids upon larval 

 growth. 



Eehinoids of known weiglit were kept for a 

 known time in a known volume of water, so tliat, 

 on determining the absolute effect produced on 

 larvae grown in this water it was possible to cal- 

 culate the relative effect produced by unit weight 

 of eehinoids kept for unit time in unit volume of 



" " Variation in Animals and Plants," 298, 

 1903. 



water. On growing larvse in water previously 

 fouled by adult eehinoids of their own species, 

 it was found that, as a mean of five observations, 

 they were diminished in relative size by 2.6 per 

 cent., whilst only 41 per cent, of the ova em- 

 ployed reached the larval stage. On growing 

 them in water fouled by eehinoids of other than 

 their own species, the larvae, as a mean of five 

 observations, were diminished by only 1.9 per cent., 

 whilst 54 per cent, of the ova reached the larval 

 stage. That is to say, the products of excretion 

 of an echinoid act more adversely both on the 

 death rate and on the growth of embryos if these 

 belong to its own species than if they belonged 

 to another species. At least this is the case with 

 Strongylocentrotus, Sphcerechinus and Echinus. 

 With two other (physiologically) less closely re- 

 lated species, viz., Arbacia pustulosa and Dorod- 

 daris papillata, it was even found that the prod- 

 ucts of excretion, so far from acting adversely on 

 growth, actually favored it. Thus Strongylocen- 

 trotus larvae grown in water fouled by these two 

 species were increased in size by respectively 4.3 

 and 1.7 per cent., whilst respectively 81 and 50 

 per cent, of the ova employed reached the pluteus 

 stage. 



Vernon" points out also that "De- 

 Varigny actually found that snails grown 

 in water in which other snails had already 

 been growing several months were dis- 

 tinctly smaller than those grown in fresh 

 water, and if the excreta of snails had been 

 added as well they were smaller still." 



The experiments of Warren^^ show that 

 water fouled by Daphnia becomes specific- 

 ally injurious to Daphnia, "for when the 

 Daphnia are fast disappearing, there may 

 be a swarm of ostracods or copepods (still 

 living healthily in the water)." 



If we were to reason from these facts to 

 the behavior of crops, such as wheat, for 

 instance, we should conclude that wheat 

 unquestionably secretes substances which 

 are toxic to itself and that the develop- 

 ment of that crop or of a subsequent one 



*" " Variation in Animals and Plants," 305, 

 1903. 



■" Vernon, " Variation in Animals and Plants," 

 309, 1903. 



