MICROPHYTOLOGY 135 



cultures has not, however, given good results in England 

 up to the present time. 



B. From a practical point of view it is very important 

 to ascertain whether a microbe produces spores. A tem- 

 perature of 70 C. kills all microbes ; whereas boiling is 

 required to kill their spores. The spores can also resist 

 dessication and oxidation far better than bacteria. The 

 microbes of plague, diphtheria and pneumonia do not form 

 spores. 



3. It has already been stated that most diseases are 

 caused by microbes. They produce not only various fevers, 

 but cholera, tetanus, leprosy, tuberculosis, etc., in which a 

 febrile temperature is not the most marked symptom. At 

 present they are being studied chiefly for the sake of finding 

 out how they cause disease, and how both men and animals 

 may be rendered insusceptible, or able to combat the disease 

 if they cannot be prevented from taking it. To what are 

 the ill-effects which follow an invasion by bacteria due? 

 They are certainly not due to the demand made by the 

 microbes upon nutrient fluids or tissues of the body, but to 

 poisons, called collectively toxins, which they either secrete 

 or cause the tissues to secrete. The secretion of the 

 microbes may be a virulent and speedy poison, or it may act 

 indirectly, leading to decomposition of the body cells and 

 juices, with consequent formation of poisonous substances. 

 In diphtheria, for example, the bacilli live in the mucous 

 membrane of the throat. The substances which they pro- 

 duce resemble ferments in many ways, particularly in their 

 sensitiveness to heat. Although not poisonous in them- 

 selves, these ferments, when absorbed into the blood, induce 

 the formation of poisons to which all the constitutional 

 symptoms are due. After the patient has recovered from 

 the local symptoms in the throat he may succumb to the 

 degeneration of his nervous system which the toxins set up. 

 What the microbe gains by destroying its host is a problem 

 as yet unsolved. It seems like a premature attempt to carry 



J 



