

LABORATORY STUDIES AND DEMONSTRATIONS. 209 



only after the leaf has been mounted for a half -hour or more 

 but when once established affords one of the most beautiful and 

 striking examples of protoplasmic motion. If Tradescantia is to 

 be used, care must be taken to have, if possible, flowers just open 

 or opening. The morning is therefore preferable for work on 

 this plant. High powers are necessary. 



In all these forms the movements may often be stimulated by 

 placing a lamp near the microscope or by cautiously warming 

 the slide over the lamp-chimney. Ciliary action is easily shown 

 in bits of the gills taken from fresh clams, mussels, or oysters, or 

 in cells scraped from the inside of the frog's O3sophagus. A 

 striking demonstration is easily given by slitting open a frog's 

 (or turtle's) O3sophagus lengthwise, pinning out flat, moistening 

 with normal salt solution, and placing tiny bits of moistened cork 

 on the surface. The progressive movement of the cork-bits i& 

 then very obvious. Muscular contractility is easily shown by 

 removing the skin from a frog's leg, dissecting out the sciatic 

 nerve, cutting its upper end, and then stimulating the lower end, 

 if possible, by contact with a pair of electrodes, otherwise by 

 pinching it with forceps. If the necessary apparatus is available 

 the regular muscle-nerve preparation may be shown (see Foster 

 and Langley's "Practical Physiology"). 



Food-stuffs Contain Energy. This may be shown (in dem- 

 onstrations) by sprinking finely powdered and thoroughly 

 dried starch, sugar, or flour upon a fire, or upon a platinum dish 

 or piece of foil heated to redness over a small flame. Oils and 

 dried and powdered albumen (proteid) may be similarly made to 

 burn with almost explosive violence if applied in a state of fine 

 division in presence of air. 



The Chemical Basis, (a) ProUids ; Coagulation ; Rigor Mor- 

 tis ; Rigor Caloris. White- of -egg may be shown (in demonstra- 

 tion) and made to coagulate in a test-tube hung down into a 

 beaker of water under which is put a llame. A thermometer in 

 the test-tube may be read off from time to time as the experi- 

 ment advances, until finally coagulation begins, when the temper- 

 ature is noted. The death-stiffening (rigor mortis) comes on 

 very quickly in frogs killed with chloroform. Heat-stiffening 

 (rigor caloris) is well shown by immersing one leg of a decapi- 

 tated frog in a beaker of water at 40 C. The other leg re- 



