234 THE AMERICAN MONTHLY [October, 



served changes made to take place. This seems very plausible, and, if 

 true, would be a case of motor activity in the cell. It w^ould, hovi^ever, 

 not be surprising to find these or any cells not exerting one or more 

 powers, and in fact the dermal cells on the underside of the body are a 

 case in point in this connection. 



Resume. — The study of the frog's skin then reveals the presence in 

 the epidermis of crowds of cells in which the power of metabolism is 

 exercised in the production of slime as well as in the constant assimila- 

 tion of substance from the blood to furnish the material for growth ; in 

 the dermis of cells jjroducing pigment responding to the surrounding, 

 and causing color change, all of which cases show the presence in these 

 cells of the powers of metabolism and irritability, and probably also of 

 motion. These cases go to show how large a problem is still before 

 the biologist before he can look at the body of an animal and by the 

 eye of the trained scientific imagination see what each kind of cell is 

 doing, and understand all the conditions of its action. Such, however, 

 is the pi'oblem, the solution of which the biological world is now ac- 

 tively seeking. 



\_To be continued.'\ 



TECHNIQUE. 



Demonstrating Tactile Papillae of Hirudo Medicinalis. — In 



order to show well, says Dr. S. Apathy in Zoologischer Anzeiger^ 

 the tactile papilla; of Hirudo medicinalis, strong spirituous solutions of 

 sublimate should be added to the water in which the starved animal is 

 kept until it moves no longer. Having been stretched out with pins, 

 ID per cent, sublimate or 70 per cent, alcohol is poured over it. This 

 makes the tactile papillae stand out from the smooth ventral surface. 



Examining Ova of Gordius. — In examining the yolk-stalk of 

 Gordius^ Sig. L. Camerano fixed this animal in one-third alcohol or 

 picric acid. Meyer's carmine stained germinal vesicle and spot well. 

 For ova the author recommends as fixative 3 per cent, nitric acid or a 

 mixture of equal parts of absolute alcohol and acetic acid, and as stain, 

 borax-carmine, or a mixture of malachite-green and vesuvin. — Mem. 

 della R. Accad. di Torino, xl {i8go.) 



Preparing Pepton-agar for Studying Pyocyanin. — M. Gessard 

 gives the following ready method for making the pepton-agar so useful 

 in studying the formation of pyocyanin. In each test-tube is placed 

 0.25 grm. of finely-chopped agar, and then 5 ccm. of neutral 2 per cent, 

 pepton solution and 5 drops of glycerine are added. The tubes are 

 then heated for some time to boiling point in a water bath in order to 

 drive out the air from the agar. After this they are sterilized for five 

 minutes at 120° C, and allowed to set in oblique position. — Annates 

 de V Institut Pasteur., iSgi., p. 6j. 



Simple Method for Sterilizing Catgut. — Mr. G. R. Fowler ster- 

 ilizes commercial catgut by boiling it for an hour in 97 per cent, alco- 

 hol. The control experiments were made with anthrax and suppura- 

 tion cocci. It was found that catgut which had been soaked in these 

 germs was rendered perfectly sterile in an hour. — JV. T. Med. Record. 



