GLOSSARY 441 



example, an atom of gold is composed of electrical bodies, protons 

 and electrons. 



Att^ium. a receiving chamber of the heart. 



Attenuated. When pathogenic bacteria are cultured under conditions 

 that reduce their virulence, they are said to be attenuated. 



AuTocATALYsis. A Catalytic reaction wherein the products of the reaction 

 increase the activity of the catalyst. 



Autosomes. Chromosomes not primarily concerned with the develop- 

 ment of sex characters. 



AxoNE. The elongated portion of the nerve cell that conducts impulses 

 away from the cell body. 



Back cross. A mating between parent and offspring. 



Bacteremia. Disease in which the disease-producing bacteria are dis- 

 seminated throughout the body of the host. See Septicemia. 



Bacteriolysin. a substance, produced by the host, that breaks down 

 and destroys invading bacteria. 



Base. A chemical compound which when in solution releases an OH 

 radical, or by reacting with water causes OH ions to form. 



Beriberi. A disease that involves the sloughing off of flesh and general 

 systemic disturbances, due to the absence of Vitamin B from the diet. 



Bilateral symmetry. The structure of the organism is such that if a 

 vertical plane were passed through its mid-line dividing the animal 

 into right and left halves, each half would be a mirror image of 

 the other. 



Bile. A secretion formed by the liver, composed of a number of sub- 

 stances that effect digestive processes. 



Binary fission. The process of reproduction in Protozoa whereby two 

 daughter cells of equal size are produced by the division of the 

 parent animal. 



Biogenetic law. The individual in its life history repeats the history 

 of the species. 



Biology. The science that includes the principles which govern matter 

 in the living state. 



Blastoccele. The cavity within the blastula. 



Blastopore. The opening formed when the hollow blastula has been 

 converted into a two-layered gastrula by the impressing of one 

 hemisphere into the other. 



Blastula. A stage in the development of Metazoa, in which the cells 

 form a hollow sphere or some modification thereof. 



