LABORATORY STUDIES AND DEMONSTRATIONS. 209 



only after tlie leaf lias been mounted for a lialf-liour or more ; 

 but when once established affords one of the most beautiful and 

 striking examples of protoplasmic motion. If Tra(.U Heard at is to 

 be used, care must be taken to have, if possi])le, tiowers just open 

 or opening. The morning is therefore preferable for work uu 

 this plant. High powers are necessary. 



In all these forms the movements may often be stinnilated l)y 

 placing a lamp near the microscope or l)y cautiously warming 

 the slide over the lamp-chhnney. 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 oesophagus. A 

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

 (or turtle's) oesophagus 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 is 

 then very obvious. Muscular contractility is easily shown l)y 

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

 nerve, cutting its upper end, and then stinmlating 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 ])owdered and ihorou^jhl y 

 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 apj^lied in a state of fine 

 division in presence of air. 



The Chemical Basis, {ci) Proteids\ Coagulation'^ Blijor Jfor- 

 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 flame. A therm(Mnetcr in 

 the test-tube may be read off from time to time as the ex])eri- 

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

 ature is noted. The death-stiffening [rigor rnortin) comes on 

 very quickly in frogs killed with chloroform. Ileat-stilfening 

 {rigor caloris) is well shown by immersing one leg of a deca])i- 

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



