18 LABORATORY DIRECTIONS IN 



blood system. Study the beating of a frog's heart in a demonstration 

 specimen. Also observe the circulation of blood in the blood vessels 

 of the web of a frog's foot. What are the formed objects in the blood? 

 Observe the thinness of the blood vessel walls. With what are they in 

 contact outside? Note differences in the size of the blood vessels. Does 

 the blood flow in a steady stream in all the vessels? Why? 



4e. Respiration and Oxidation. Oxidation with the liberation of 

 energy takes place in the tissues. The oxygen needed in the process is 

 supplied through the lungs in higher forms and usually through gills in 

 lower forms of animals. Carbon dioxide which is formed during the 

 process is eliminated through the same organs. Presence of carbon 

 dioxide in the expired air may be demonstrated by the following experi- 

 ment which can be performed by each student. Put a little lime water, 

 Ca(OH) 2 , in a test-tube and blow through it with a glass tube or blow 

 pipe. Note results. The C02 in the expired air combines with the 

 Ca(OH) 2 to form an insoluble substance calcium carbonate, CaCOa. Now 

 pass some ordinary laboratory air through a fresh supply of lime water by 

 means of a large rubber bulb and a glass tube. Results? Conclusion? 



4/. Excretion. Most of the nitrogenous waste products are removed 

 by the kidneys. Study a cross-section of the kidney of a frog. The kid- 

 ney is made up of small tubes, much coiled, and the section cuts these 

 tubes at all possible angles. Note that the tubules are more distinct in 

 some parts of the section than in others. From a chart learn the arrange- 

 ment of the tubes and their connection with the ducts leading from the 

 kidney. 



In one part of the section find a number of rounded bodies, the glom- 

 eruli. These lie within small capsules known as Bowman's capsules 

 at the end of the tubules. These are difficult to make out in the sections 

 and a chart should be consulted. A Bowman's capsule and its glomeru- 

 lus are together known as a Malpighian corpuscle. The glomeruli are 

 coiled blood vessels, and the yellowish cells in them are red blood cells. 

 Find red blood cells elsewhere in the section, outside of the glomeruli. 

 In a demonstration specimen of an injected kidney note again the glom- 

 eruli and the numerous blood vessels in the rest of the kidney. The 

 tubules are not easily made out in this section. What function may the 

 close proximity of tubules and blood vessels serve? What physical 

 phenomenon may account for the elimination of waste by the tubules 

 of the kidney? 



From your reading be sure you understand the main facts of the struc- 

 ture of the kidney and the functions of the kidney. 



C. SUMMARY 



In your summary of the functions of protoplasm compare the func- 

 tions of one-celled animals and of other single cells with the functions 



