PRINCIPLES OF ANIMAL BIOLOGY 15 



water. Examine with high magnification and determine the structure 

 of the food vacuoles. What proportion of the vacuole is liquid and what 

 proportion is solid material? Where are the food vacuoles found? 

 What accounts for their distribution? Are the carmine vacuoles evenly 

 distributed? If not where are they most abundant? Do you observe 

 any difference in the various food vacuoles? What may be the object 

 of the liquid in the vacuoles? What may be its source? 



Neutral red gives an opportunity to determine the nature of some of 

 the chemical processes taking place in the vacuoles since it stains acid 

 substances red and alkaline ones yellow. To prove this put a drop of 

 weak alkaline solution (NaOH) and another drop of weak acid solution 

 (HC1) at opposite ends of a slide resting on a white background. Add 

 a drop of neutral red (0.001 per cent, solution) to each of the drops on the 

 slide and note results. 



Mount a fresh slide of paramecia and put a drop of neutral red along 

 the edge of the cover-glass. This will reach the paramecia after a few 

 minutes, with the usual result that some of the food vacuoles are stained 

 red, others will be found to be colorless, and still others will have a pale 

 yellowish tinge. What does this suggest as to the nature of the contents 

 of the three kinds of vacuoles? What is the source of the substances 

 indicated in the vacuoles? Other substances whose action may account 

 for the digestion of the food in the vacuoles may be inferred at the end of 

 the exercise. 



2c. Absorption. After food is rendered soluble by digestion it is 

 absorbed by the surrounding protoplasm. This process cannot readily 

 be demonstrated. How may it take place in Paramecium? 



2d. Respiration and Oxidation. This function is also difficult to 

 demonstrate in single cells. In Paramecium oxygen is taken in directly 

 through the surface of the body and carbon dioxide is given off in the same 

 way. What provision, if any, is made for bringing in oxygen to the vari- 

 ous parts of the body and for taking carbon dioxide out to the surface? 

 How is a constant supply of fresh water brought to the animal? 



2e. Excretion. Excretion takes place in Paramecium by means of 

 two clear pulsating vacuoles. Mount some paramecia and observe the 

 vacuoles in a quiet specimen. Note that they increase in size and dis- 

 appear at intervals. Where are they located? Observe the radiating 

 canals around them. At what stage in the pulsation of the vacuoles are 

 these canals most conspicuous? What do the vacuoles contain? What 

 is the relation of the canals to the vacuoles? What becomes of the 

 contents of the vacuoles when they disappear? 



B. FUNCTIONS OF TISSUES AND ORGANS 



The cell in one-celled organisms has a generalized function. In 

 multicellular organisms different cells have become specialized to perform 



