Mabch 25, 1910] 



SCIENCE 



469 



to an increase in irritability, such that a stimulus 

 that is too weak to cause a response when applied 

 singly, will, upon repetition, prove effective. The 

 observ'ations here reported were made on the 

 muscles of certain species of invertebrates, namely, 

 Cyanea arotica, Aurelia flavidula, Homarus amer- 

 icanus, Carcinus mcenas, Cancer irroratus and 

 Cancer borealis. The major part of the work was 

 done on Cyanea arctica, Carcinus mcenas and 

 Homarus am^ricanus, the muscles of all of which 

 possess a marked power of summating stimuli. 

 It was found that the irritability of the muscles 

 can be raised by the administration to them of 

 carbon dioxide or lactic acid in great dilution. 

 Solutions of lactic acid of from 1/100 gram 

 molecular to 1/6400 gm. were used, the best 

 results being obtained by the use of 1/1600 gm. 

 It was found possible by these reagents to change 

 the threshold of stimulation so that a muscle 

 responded by contractions to shocks from an in- 

 ductorium which previously were unable to elicit 

 responses. Thus by the injection in small quan- 

 tities of agents which in larger quantities depress 

 the action of muscle, it is possible to enable the 

 muscle to respond to stimuli previously ineffect- 

 ive. Gotschlieh found that subminimal stimula- 

 tion of muscle renders it acid in reaction, even 

 though no contractions occur. The conclusion, 

 therefore, seems to be justified that summation 

 of stimuli is due to a rise in irritability, brought 

 about by the action on the living substance of 

 small quantities of certain products of metabolism, 

 especially carbon dioxide and lactic acid, the same 

 substances which in larger quantities are impor- 

 tant factors in fatigue. 



Rates of Regeneration in Various Salt Solutions, 

 and the Influence of Regenerating Tissue on the 

 Animal Body: Chables R. Stock a rd, Cornell 

 Medical School. 



The processes of regenerative growth in the 

 salamander are favorably affected by weak doses 

 of KCl while CaCl. inhibits the rate of growth 

 and differentiation of the part. Solutions of 

 MgCL also inhibit growth and differentiation, yet 

 not so decidedly as the CaClj. Mixtures of half 

 doses of CaClj and MgClj do not influence either 

 growth rate or differentiation. 



The influence of a salt solution is largely de- 

 pendent upon the salt to which the animal has 

 been previously subjected, even though some time 

 may have elapsed since the former treatment was 

 applied. Animals that have regenerated at a fair 

 rate in solutions of KCl are less depressed by 



treatment with CaClj than others which have not 

 been treated with KCl. 



When animals are unfed they decrease in body 

 size. This decrease is greater in regenerating in- 

 dividuals, and the larger the amount of tissue an 

 individual is regenerating the more rapidly does 

 it decrease in size. The new regenerating tissue 

 grows at a vigorous rate on account of its ex- 

 cessive capacity for the appropriation of nutri- 

 ment from the old body tissues, and it is this 

 fact that causes the body to decrease in size and 

 become weak and emaciated. A closely similar 

 action is seen in the behavior of certain malignant 

 growths. 



On the Structure and Regeneration of the Epi- 

 dermal Layer in some Siliceous Sponges: H. V. 

 Wilson, University of North Carolina. (Pre- 

 sented by title.) 



The epidermal layer in two monactinellid 

 sponges (Stylotella and Reniera) was studied. 

 Various histological methods were employed. The 

 epidermis does not consist of flat epithelium cells 

 (pinacocytes), but is a continuous, thin sheet of 

 protoplasm studded with nuclei and entirely with- 

 out cell boundaries. It is a syncytium. 



The pores are the superficial apertures of very 

 short canals (pore-canals) which perforate the 

 dermal membrane. Closure of the pore is brought 

 about by an extension (pore-membrane) of the 

 thin epidermal layer over the pore-canal. The 

 pore-membrane in Stylotella from the start is 

 continuous and diaphragm-like. In Reniera the 

 pore-membrane in the early stages of pore-closure 

 exhibits active, amoeboid change? of shape and 

 position. 



In Stylotella a new epidermis develops over a 

 cut surface in the course of a day. It is formed 

 by the cells of the mesenchyme, which are already 

 interconnected by slender processes. The mesen- 

 chyme cells crowd to the surface and flatten out. 

 At this time they are close together and connected 

 by a reticulum of delicate, protoplasmic strands. 

 Union between the cells then becomes perfect, 

 their boundaries disappearing. 

 Wound Reparation and Polarity in Tentacles of 

 Sagartia: Hebbebt W. Rand, Harvard Univer- 

 sity. 



If a distal piece is cut from a tentacle of Cortr 

 dylactis or other large actinians, the wall at the 

 cut edge of the stump immediately bends inward 

 slightly. Then a broad zone of wall at the cut 

 edge contracts until its lumen is obliterated, 

 so that the distended stump, now functionally 



