164 VETERINAEY STATE BOARD 



(b) a poisonous product elaborated by microorganisms ; (c) a serum 

 destructive to bacteria ; (d) a serum containing a lysin destructive 

 to a species of bacteria ; (e) a toxin excreted by a microorganism, 

 and which can be recovered by filtration from, a culture without 

 destruction of the producing agent; (f) a toxin elaborated by a 

 microorganism within its substance, and which becomes free only 

 after destruction of the producing agent. 



What do you understand by negative phase? 



The temporary lowering of the opsonic index, following an 

 injection of a bacillary vaccine. It is followed by the positive 

 phase in which the opsonic index is raised and a relief from the 

 general symptoms of the disease is observed. 



What is meant by the optimum, maximum and minimum of tempera- 

 ture of a germ? 

 All bacteria grow best at a certain temperature, about 38° C, 

 called the optimum. Some will grow at a, much lower and some at 

 a much higher temperature. The lowest point at which the germ 

 win grow is called the minimum, and the highest point, the maxi- 

 mum temperature of the germ. 



What do you understand by Gram-positive and Gram-negative? 



This refers to Gram's diiferential method of staining bacteria. 

 The specimen is first placed in aniline gentian violet, then rinsed 

 in water and immersed in Gram's solution of iodine (iodine 1, potas- 

 sium iodide 2, water 300), again rinsed in water and placed for a 

 few minutes in strong alcohol, washed again and dipped in dilute 

 eosin solution. The bacteria that are stained a deep-violet by this 

 method are called Gram-positive; those that are decolorized and 

 take on the counter-stain are Gram-negative. 



How do bacteria produce disease? 



By their irritating local action and by the production of toxins. 



Define immunity and give varieties. 



A state in which the body is resistant to disease. 1. Natural 

 immunity, possessed by all the individuals of a class, by reason of 

 age or racial peculiarity. Cattle are naturally immune to glanders. 

 2. Acquired immunity, obtained by having overcome an attack of a 

 pathogenic microorganism (active), or as a result of the injection 

 of a serum from an animal which has acquired an active immunity 

 against the organism in question (passive). 



What disease is caused by tinea tonsurans ? 

 Ringworm. 



